Design a Block Node Simulator/gRPC Server in process to simulate response codes etc.

[derektriley]

This issue is to design and research (possibly implement if time permits) a gRPC Server "stub" which can be in process on the consensus node for testing purposes. The server stub needs to be present to not cause the consensus node to think it cannot connect to a block node.

Things to think about including:

• Block Acknowledgements
  -- Perhaps just immediately acknowledge upon receiving a BlockProof item within the BlockItemSet.
• Mechanism to trigger a number of PublishStreamResponseCodes to be able to write tests for consensus node to block node communication behaviors.