[grpc_clients] add connect_timeout to shared grpc client

Summary: by default, the shared grpc client will try to connect indefinitely to the endpoint url. we should time out after 1 second if we're unable to connect.

Test Plan: repro'd ENG-6052 and then added the time out and confirmed that the client only waited 1 second before giving up

Reviewers: ashoat, bartek

Reviewed By: bartek

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10329