[validator] Let me customize the error code

[jinleileiking]

				return nil, grpc.Errorf(codes.InvalidArgument, err.Error())

I want to not use codes.InvalidArgument =3, so give me a opt to let me choose what errcode to return

[mwitkow]

Happy to accept a PR that introduces an option to it.

[bwplotka]

This is pretty old and we know have v2 code with different structure. Let us know if this is still important, we can reopen.