Module of client/server GRPC proto files, as well as generated and utility code for mix-in by client and servers. The generated GRPC code has the client and server service stubs in the one class and the protobuf messages used in communication are defined here. We want to avoid the client depending (or bundling) server-side code other than the bare protobuf api description and messages (and vice-versa) so have the upstream server and client modules depend on this module alone and implement their end of the communication without having to have any other dependencies on each other (An important Relational goal is a light-weight client loosely coupled to the backend so the backend and client can be evolved fairly independently).