Mirror: #416

Create e2e testing using a gRPC generated server:

1. Integrate protobuf bazel rules with our tests + add simple echo service: ttps://github.com/kotlin: add simple grpc echo server/client #473
2. Build java library with JNI: hhttps://github.com/java: add bazel rules for separate java jni lib #474
3. Implement gRPC codec with end to end testing for higher confidence: kotlin: grpc codec #472