[shared] introduce ping client method in grpc_clients crate
Summary: this is the method that clients will call periodically to make sure their code version is supported
Test Plan: tested in next diff by calling client method from js on native
Reviewers: bartek, michal
Reviewed By: bartek
Subscribers: ashoat, tomek, wyilio
Differential Revision: https://phab.comm.dev/D9812