[gRPC] Bugs in streaming with Empty Type.

[daksithj]

There are some multiple bugs in streaming involving an Empty request or response.

1. In server streaming, if the request message is of Empty type, the following error shows up in the client side.
   error {ballerina/grpc}InternalError message=Error while processing the request message. Connection Sub type not supported

2. In client streaming, there is no way to send an Empty type response back to the client (neither caller->send() nor caller->complete() seems to do the job).

3. When generating a service sample for streaming (--mode=service) with Empty requests, incorrect function parameters are generated as follows.
   resource function UnaryStream(grpc:Caller caller, value) {
   // Implementation goes here.
   }

4. When generating a service sample for client streaming, the generated "name" field in the service config is incorrect. The resource name is generated here, whereas it should be the service name.
   @grpc:ServiceConfig {
   name: "service name should be generated instead here",
   clientStreaming: true
   }
   or else the following error shows up:
   error: {ballerina/grpc}InternalError message=Error when initializing service register builder. Couldn't find the service descriptor for the service: resourceName

[daneshk]

Issue 03 and 04 are fixed in the master branch. We need to check issue 01 and 02.