Issue:
Bug: [REFACTOR] : [Paypal] Error Message For Connector Implementation



### :memo: Feature Description

- In terms of errors, we are currently throwing a 'not supported' message, which shouldn't be the case as we are yet to decide on the implementation.


### :hammer: Possible Implementation

- In order to manage payment methods that are not implemented by Hyperswitch or yet to be implemented, the connector transformers file should make use of the NotImplemented ConnectorError enum variant.
- By doing so, we will throw same error message for all the Connector Implementation 
- You can check this PR for further reference https://github.com/juspay/hyperswitch/pull/2831


:bookmark: Note: All the changes needed should be contained within `hyperswitch/crates/router/src/connector/`


### :package: Have you spent some time checking if this feature request has been raised before?

- [X] I checked and didn't find a similar issue

### :package: Have you read the Contributing Guidelines?

- [X] I have read the [Contributing Guidelines](https://github.com/juspay/hyperswitch/blob/main/docs/CONTRIBUTING.md)

### :sparkles: Are you willing to submit a PR?


Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
Refactored `NotSupported` Error calls to `NotImplemented` in the Paypal transformer.

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->
Changes are here: `crates/router/src/connector/paypal/transformer.rs`

## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
-->
These changes fix the open issue #2858.


## How did you test it?
<!--
Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->
Make any payment for Paypal connector for any PM which is not implemented, and see for the error message - it should be payment method not implemented


## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Testing:

Make any payment for Paypal connector for any PM which is not implemented, and see for the error message - it should be payment method not implemented

Patch:
diff --git a/crates/router/src/connector/paypal/transformers.rs b/crates/router/src/connector/paypal/transformers.rs
index baf8f48279d..88595585fe1 100644
--- a/crates/router/src/connector/paypal/transformers.rs
+++ b/crates/router/src/connector/paypal/transformers.rs
@@ -396,11 +396,9 @@ fn get_payment_source(
         | BankRedirectData::Trustly { .. }
         | BankRedirectData::OnlineBankingFpx { .. }
         | BankRedirectData::OnlineBankingThailand { .. } => {
-            Err(errors::ConnectorError::NotSupported {
-                message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                connector: "Paypal",
-            }
-            .into())
+            Err(errors::ConnectorError::NotImplemented(
+                utils::get_unimplemented_payment_method_error_message("Paypal"),
+            ))?
         }
     }
 }
@@ -544,10 +542,9 @@ impl TryFrom<&PaypalRouterData<&types::PaymentsAuthorizeRouterData>> for PaypalP
                 | api_models::payments::WalletData::WeChatPayQr(_)
                 | api_models::payments::WalletData::CashappQr(_)
                 | api_models::payments::WalletData::SwishQr(_) => {
-                    Err(errors::ConnectorError::NotSupported {
-                        message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                        connector: "Paypal",
-                    })?
+                    Err(errors::ConnectorError::NotImplemented(
+                        utils::get_unimplemented_payment_method_error_message("Paypal"),
+                    ))?
                 }
             },
             api::PaymentMethodData::BankRedirect(ref bank_redirection_data) => {
@@ -611,10 +608,9 @@ impl TryFrom<&PaypalRouterData<&types::PaymentsAuthorizeRouterData>> for PaypalP
             | api_models::payments::PaymentMethodData::Crypto(_)
             | api_models::payments::PaymentMethodData::Upi(_)
             | api_models::payments::PaymentMethodData::CardToken(_) => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -629,10 +625,9 @@ impl TryFrom<&api_models::payments::CardRedirectData> for PaypalPaymentsRequest
             | api_models::payments::CardRedirectData::Benefit {}
             | api_models::payments::CardRedirectData::MomoAtm {}
             | api_models::payments::CardRedirectData::CardRedirect {} => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -651,10 +646,9 @@ impl TryFrom<&api_models::payments::PayLaterData> for PaypalPaymentsRequest {
             | api_models::payments::PayLaterData::WalleyRedirect {}
             | api_models::payments::PayLaterData::AlmaRedirect {}
             | api_models::payments::PayLaterData::AtomeRedirect {} => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -669,10 +663,9 @@ impl TryFrom<&api_models::payments::BankDebitData> for PaypalPaymentsRequest {
             | api_models::payments::BankDebitData::SepaBankDebit { .. }
             | api_models::payments::BankDebitData::BecsBankDebit { .. }
             | api_models::payments::BankDebitData::BacsBankDebit { .. } => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -696,10 +689,9 @@ impl TryFrom<&api_models::payments::BankTransferData> for PaypalPaymentsRequest
             | api_models::payments::BankTransferData::MandiriVaBankTransfer { .. }
             | api_models::payments::BankTransferData::Pix {}
             | api_models::payments::BankTransferData::Pse {} => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -724,10 +716,9 @@ impl TryFrom<&api_models::payments::VoucherData> for PaypalPaymentsRequest {
             | api_models::payments::VoucherData::FamilyMart(_)
             | api_models::payments::VoucherData::Seicomart(_)
             | api_models::payments::VoucherData::PayEasy(_) => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }
@@ -740,10 +731,9 @@ impl TryFrom<&api_models::payments::GiftCardData> for PaypalPaymentsRequest {
         match value {
             api_models::payments::GiftCardData::Givex(_)
             | api_models::payments::GiftCardData::PaySafeCard {} => {
-                Err(errors::ConnectorError::NotSupported {
-                    message: utils::SELECTED_PAYMENT_METHOD.to_string(),
-                    connector: "Paypal",
-                }
+                Err(errors::ConnectorError::NotImplemented(
+                    utils::get_unimplemented_payment_method_error_message("Paypal"),
+                )
                 .into())
             }
         }