Add Container Registry Event API annotation
The POST /container_registry_event/events
endpoint was added in !27001 (merged) but is undocumented. This adds the missing documentation since we would like the generated OpenAPI spec to cover as many endpoints as possible for proper dynamic testing coverage.
The OpenAPI V2 documentation will be used for dogfooding API fuzzing as per #372422 (closed) and the OpenAPI autogeneration &8926.