Issue:
Bug: [BUG] API Handler missing for Disputes - Retrieve Evidence endpoint



### Bug Description

API Handler is missing (got removed somehow) for the `Disputes - Retrieve Evidence` endpoint. This results in a Content Not Found error (404).

### Expected Behavior

The endpoint is implemented and working fine. It should work as expected.

### Actual Behavior

The following error is being thrown when hitting the said endpoint : 

`{
    "error": {
        "type": "invalid_request",
        "message": "Unrecognized request URL",
        "code": "IR_02"
    }
}`

### Steps To Reproduce

Hit the `Disputes - Retrieve Evidence` endpoint.

### Environment

Local

### Have you spent some time to check if this bug has been raised before?

- [X] I checked and didn't find 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

## Description
<!-- Describe your changes in detail -->
 This PR adds the missing API Handler for the mentioned endpoint.

## 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 its an obvious bug or documentation fix
that will have little conversation).
-->
This PR solves [this](https://github.com/juspay/hyperswitch/issues/1513) issue.

## 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)?
-->
Locally using Postman.

## 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 submitted code

Testing:

Locally using Postman.

Patch:
diff --git a/crates/router/src/routes/app.rs b/crates/router/src/routes/app.rs
index f153850ce87..35e366ac6f3 100644
--- a/crates/router/src/routes/app.rs
+++ b/crates/router/src/routes/app.rs
@@ -464,6 +464,10 @@ impl Disputes {
                     .route(web::post().to(submit_dispute_evidence))
                     .route(web::put().to(attach_dispute_evidence)),
             )
+            .service(
+                web::resource("/evidence/{dispute_id}")
+                    .route(web::get().to(retrieve_dispute_evidence)),
+            )
             .service(web::resource("/{dispute_id}").route(web::get().to(retrieve_dispute)))
     }
 }