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!
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>,
 }
 

## 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
<!--
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).
-->


## 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)?
-->


## 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
