* Move gRPC error intercetpors to api/utils/grpc/interceptors.
* Use error interceptors in api client and mock server.
* Apply suggestions from CR.
* Unwrap FromGRPC errors in middleware.
* Use gRPC auth service in tests instead of external example service.
* It's gRPC!!!
* Fix unit test.
* Add error interceptor to proxy client.
* Fix merge conflict.