Issue: [FEATURE] Add delete merchant account endpoint in v2

### Feature Description

[FEATURE] Add delete merchant account endpoint in v2

### Possible Implementation

Add a new endpoint in routes for delete merchant account in v2

### 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!

Resolution: <think>
PR Context:
- Title: feat(merchant): Add delete endpoint for merchant accounts v2
- Merged: None
- Files changed: 4 files
- Commits: 2 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
- Add merchant account delete route in ```app.rs```
- Update openapi spec to include the newly added route


### Additional Changes

- [x] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modif
</think>

To implement this, you'll need to modify:


(No detailed commit information available)