### What problem does this PR solve?
implement delete, rebuild api for connector
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
implement create_connector API
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
## Summary
- Add Go REST support for `GET /api/v1/connectors/:connector_id`.
- Reuse the Python API behavior by returning the connector only when the
current user can access its tenant.
- Add focused handler coverage for success and unauthorized responses.
Co-authored-by: Jin Hai <haijin.chn@gmail.com>
