metrics: add running metrics for grpc

[bufferflies]

close: #640 the metrics after this pr

[bufferflies]

It's better not to directly introduce Prometheus. There are two ways to do it:

1. Use the monitoring infrastructure that comes with grpc (C++ counter/histogram), like this PR Support collecting gRPC core metrics #625.
2. Add a feature to make Prometheus an optional dependency.

good idea, I had add new feature("promethes ") to check the dependency.

[bufferflies]

/ping @overvenus

[glorv]

@overvenus PTAL