Define OSS protos for UpstreamMessageService rpc which defines a way
to send an upstream message to a controller (across multi-hops if
needed).
Implement OSS versions of both workers and controllers for the
UpstreamMessageService. The upstream requests/responses are encrypted
using the originating worker's NodeCredential's key.
The worker always forwards the request upstream.
The controller attends to find a registered UpstreamMessageHandler to
handle the msg; if none if found, then an Unimplemented status error
is returned.
Jim
Todd