Issue:
Bug: [REFACTOR] : [Stax] 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 -->

- [x] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->


### 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`
-->


## Motivation and Context
Resolves #2862


## 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)?
-->
No test cases required. As In this PR only error message have been changed from Not Supported error message to NotImplemented error message.

## 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:

No test cases required. As In this PR only error message have been changed from Not Supported error message to NotImplemented error message.

Patch:
diff --git a/crates/router/src/connector/stax/transformers.rs b/crates/router/src/connector/stax/transformers.rs
index bb37bf1fc9e..5aa0949a09c 100644
--- a/crates/router/src/connector/stax/transformers.rs
+++ b/crates/router/src/connector/stax/transformers.rs
@@ -63,10 +63,9 @@ impl TryFrom<&StaxRouterData<&types::PaymentsAuthorizeRouterData>> for StaxPayme
         item: &StaxRouterData<&types::PaymentsAuthorizeRouterData>,
     ) -> Result<Self, Self::Error> {
         if item.router_data.request.currency != enums::Currency::USD {
-            Err(errors::ConnectorError::NotSupported {
-                message: item.router_data.request.currency.to_string(),
-                connector: "Stax",
-            })?
+            Err(errors::ConnectorError::NotImplemented(
+                utils::get_unimplemented_payment_method_error_message("Stax"),
+            ))?
         }
         let total = item.amount;
 
@@ -119,10 +118,9 @@ impl TryFrom<&StaxRouterData<&types::PaymentsAuthorizeRouterData>> for StaxPayme
             | api::PaymentMethodData::GiftCard(_)
             | api::PaymentMethodData::CardRedirect(_)
             | api::PaymentMethodData::Upi(_)
-            | api::PaymentMethodData::CardToken(_) => Err(errors::ConnectorError::NotSupported {
-                message: "SELECTED_PAYMENT_METHOD".to_string(),
-                connector: "Stax",
-            })?,
+            | api::PaymentMethodData::CardToken(_) => Err(errors::ConnectorError::NotImplemented(
+                utils::get_unimplemented_payment_method_error_message("Stax"),
+            ))?,
         }
     }
 }
@@ -270,10 +268,9 @@ impl TryFrom<&types::TokenizationRouterData> for StaxTokenRequest {
             | api::PaymentMethodData::GiftCard(_)
             | api::PaymentMethodData::CardRedirect(_)
             | api::PaymentMethodData::Upi(_)
-            | api::PaymentMethodData::CardToken(_) => Err(errors::ConnectorError::NotSupported {
-                message: "SELECTED_PAYMENT_METHOD".to_string(),
-                connector: "Stax",
-            })?,
+            | api::PaymentMethodData::CardToken(_) => Err(errors::ConnectorError::NotImplemented(
+                utils::get_unimplemented_payment_method_error_message("Stax"),
+            ))?,
         }
     }
 }