[HachemJ]

Brief summary of changes

This PR adds REST API support for candidate identifiers, including new endpoints, a response view, and updates to the existing candidate endpoint. The OpenAPI schema has also been updated to document these changes.

This PR depends on #11212 and focuses on the API layer, while identifier generation, validation, and database changes are handled in the preceding PRs.

Testing instructions (if applicable)

1. Verify that the candidate identifier endpoints return the expected responses.
2. Confirm that candidate identifiers can be retrieved through the API.
3. Check that the new endpoints are correctly documented in the OpenAPI schema.