[Tensorpipe Agent] Implementing getMetrics with currently available metrics (#37980)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37980
This implements `TensorPipeAgent::getMetrics` with the metrics currently available. Will add other metrics such as Client/Server Active Calls once time outs are implemented.
ghstack-source-id: 103624005
Test Plan: CI
Differential Revision: D21439184
fbshipit-source-id: 8a15df58cc23cdf954e604c0f806877ba111e0a6
