Issue:
Bug: Fix deserialization errors for sdk_eligible_payment_methods



### Feature Description

fix deserialization errors for sdk_eligible_payment_methods

### Possible Implementation

A small fix

### Have you spent some time checking if this feature request has been raised before?

- [X] I checked and didn't find a similar issue

### Have you read the Contributing Guidelines?

- [X] I have read the [Contributing Guidelines](https://github.com/juspay/hyperswitch/blob/main/docs/CONTRIBUTING.md)

### Are you willing to submit a PR?

Yes, I am 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 -->
Fix for deployment


### 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
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If it fixes an open issue, please link to the issue here.

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can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
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## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
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## 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`
- [ ] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:

Patch:
diff --git a/config/config.example.toml b/config/config.example.toml
index b5585a84b32..f0dad483c65 100644
--- a/config/config.example.toml
+++ b/config/config.example.toml
@@ -615,4 +615,4 @@ refunds = "hyperswitch-refund-events"
 disputes = "hyperswitch-dispute-events"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
\ No newline at end of file
+sdk_eligible_payment_methods = "card"
\ No newline at end of file
diff --git a/config/deployments/integration_test.toml b/config/deployments/integration_test.toml
index fe47b10b543..faf3bb7f466 100644
--- a/config/deployments/integration_test.toml
+++ b/config/deployments/integration_test.toml
@@ -321,4 +321,4 @@ connectors_with_webhook_source_verification_call = "paypal"         # List of co
 keys = "user-agent"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
\ No newline at end of file
+sdk_eligible_payment_methods = "card"
\ No newline at end of file
diff --git a/config/deployments/production.toml b/config/deployments/production.toml
index 3135b3d5682..f564b976bc0 100644
--- a/config/deployments/production.toml
+++ b/config/deployments/production.toml
@@ -332,4 +332,4 @@ connectors_with_webhook_source_verification_call = "paypal"     # List of connec
 keys = "user-agent"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
\ No newline at end of file
+sdk_eligible_payment_methods = "card"
\ No newline at end of file
diff --git a/config/deployments/sandbox.toml b/config/deployments/sandbox.toml
index 921301ebd6f..35c8a2ba3d6 100644
--- a/config/deployments/sandbox.toml
+++ b/config/deployments/sandbox.toml
@@ -336,4 +336,4 @@ connectors_with_webhook_source_verification_call = "paypal"        # List of con
 keys = "user-agent"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
\ No newline at end of file
+sdk_eligible_payment_methods = "card"
\ No newline at end of file
diff --git a/config/development.toml b/config/development.toml
index db7f1ed93f4..3f05872bc6a 100644
--- a/config/development.toml
+++ b/config/development.toml
@@ -617,4 +617,4 @@ refunds = "hyperswitch-refund-events"
 disputes = "hyperswitch-dispute-events"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
+sdk_eligible_payment_methods = "card"
diff --git a/config/docker_compose.toml b/config/docker_compose.toml
index 702d134f2d5..9fd22f46707 100644
--- a/config/docker_compose.toml
+++ b/config/docker_compose.toml
@@ -476,4 +476,4 @@ refunds = "hyperswitch-refund-events"
 disputes = "hyperswitch-dispute-events"
 
 [saved_payment_methods]
-sdk_eligible_payment_methods = ["card"]
\ No newline at end of file
+sdk_eligible_payment_methods = "card"
\ No newline at end of file
diff --git a/crates/router/src/configs/settings.rs b/crates/router/src/configs/settings.rs
index 12ce9c39d6f..adc09fb55af 100644
--- a/crates/router/src/configs/settings.rs
+++ b/crates/router/src/configs/settings.rs
@@ -167,7 +167,9 @@ pub struct PaymentMethodAuth {
 }
 
 #[derive(Debug, Deserialize, Clone, Default)]
+#[serde(default)]
 pub struct EligiblePaymentMethods {
+    #[serde(deserialize_with = "deserialize_hashset")]
     pub sdk_eligible_payment_methods: HashSet<String>,
 }