Proposal

Nowadays, gRPC services are getting more adopted and preferred over traditional REST services.
To expose gRPC service metrics, it usually requires embedded web server running aside to host REST endpoint configured to be scrapped by Prometheus.
This propose is to develop proto file that describes the rpc method, it's request and response messages.
Prometheus team will use the gRPC client to scrap the metrics exposed by gRPC server developed based on the same proto file.