## Summary
This PR adds API documentation for the contact merge endpoint:
`POST /api/v1/accounts/{account_id}/actions/contact_merge`
This endpoint allows merging two contacts into one. The base contact
survives and receives all data from the mergee contact, which is then
deleted.
## Changes
- Added `swagger/paths/application/contacts/merge.yml` with complete
endpoint documentation
- Updated `swagger/paths/index.yml` to include the new endpoint
## Related Issues
Closeschatwoot/docs#243
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Co-authored-by: Pranav <pranav@chatwoot.com>