Golang chaincode gRPC server

The chaincode will run as a server when "chaincode.servermode" property is set to true.

Phase 1 - use existing single-stream protocol
On receiving a connection it will launch into the old "chaincode as client" protocol flow on the established stream.

Phase 2 - Invoke as a separate RPC call
Each invoke will be a separate RPC call. This has advantages of simplicity and improved performance. However this is more disruptive from code change and refactoring point of view.

The two phases should be seamless for devops or enduser. Phase 2 can be done later once phase 1 proves out the "chaincode as server" concept.