[FIX]: Take merchant ID from headers in API Key Revoke (v2)

For `API Key - Revoke` in v2, the merchant ID is currently being passed in the path. We need to instead read the `X-Merchant-ID` header to get the merchant ID.
<think>
PR Context:
- Title: fix(router): Take merchant ID from headers in API Key - Revoke (v2)
- Merged: 2025-08-05T08:25:19Z
- Files changed: 2 files
- Commits: 1 commits

Implementation approach:
## 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 -->
- Removed merchant ID from path in `API Keys - Revoke`
- Changed auth to read merchant ID from headers

### Additional Changes

- [x] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies ap
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix(router): Take merchant ID from headers in API Key - Revoke (v2) (#8808)
Files to modify:


**crates/router/src/core/api_keys.rs**
  Modify existing code

**crates/router/src/routes/api_keys.rs**
  Modify existing code
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