* Wait for acknowledgment when sending message to gRPC channel
* Add CancellationToken parameters to API surface
* Clean up the Hello sample, support Aspire 9.0, & fix shutdown
Remove unused code, refactor AgentBase and AgentWorker/Runtime to use interfaces throughout to enable future implementation of alternate runtimes and separation of the gprpc service from Agent Base (for future in-memory version).
Also adds the missing RegisterAgentResponse methods