Issue:
Bug: Update open-api spec of /relay request to make the data untagged enum



Update open-api spec of /relay request to make the data untagged enum

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [x] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
Update open-api spec of /relay request to make the data untagged enum.

### 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`
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## 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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<img width="1616" alt="image" src="https://github.com/user-attachments/assets/4ba7d3d6-9fcd-4a29-a7ff-62f0a5abda22" />


## 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


Testing:

<img width="1616" alt="image" src="https://github.com/user-attachments/assets/4ba7d3d6-9fcd-4a29-a7ff-62f0a5abda22" />

Patch:
diff --git a/crates/openapi/src/routes/relay.rs b/crates/openapi/src/routes/relay.rs
index 9100bf47f75..180fed66492 100644
--- a/crates/openapi/src/routes/relay.rs
+++ b/crates/openapi/src/routes/relay.rs
@@ -13,8 +13,10 @@
                     "connector_id": "mca_5apGeP94tMts6rg3U3kR",
                     "type": "refund",
                     "data": {
-                        "amount": 6540,
-                        "currency": "USD"
+                        "refund": {
+                            "amount": 6540,
+                            "currency": "USD"
+                        }
                     }
                 })
             )