Creates framework for new API messaging

- Creates IContextHubClientCallback as a proxy to invoke
messaging/life-cycle callbacks for the client.
- Creates IContextHubClient as a proxy to send messages at the client
side.
- Creates a ContextHubClientManager at the service to manage
clients and messaging/lifecycle event callbacks.
- Implements generation of clients at ContextHubManager and sending
messages through ContextHubClient

Bug: 67734082
Test: make from root
Change-Id: I3a7e69f89cd70ea59160a651dcdb729e18027e9f