Protocol Buffer definitions for PubSub.

Before contributing to this project, you need to install:

1. The protoc tool (Protocol Buffer compiler)

2. The required compiler plugins:

$ go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
$ go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest

To update generated files:

$ make generate_grpc_code