Client-Streaming gRPC Calls

Client-streaming calls work by having a client send a stream of messages to the server. Then, when the client closes the stream, the server returns a single object as the response. This functionality is useful in situations where a client would need to send periodic updates to the server. For example, the client might be an IoT device that sends some sensor metrics to the server. Being able to write those into a stream saves bandwidth because we won't have to make a separate request for every metric being sent.