add health service proto def and implementation

[vtolstov]

something like:

• NewMeterService() => /metrics endpoint with proto/http endpoint rpc method
• NewHealthService() => /live , /ready /healthz ( see https://github.com/grpc/grpc/blob/master/doc/health-checking.md )
• NewProfileSerice() => /pprof stuff

where to place such stuff

[vtolstov]

done for health and metrics