go/chromeos-skylab-doc / go/cros_test_on_atp will deprecate the autotest RPC layer.

As a first step  issue 672231  attempts to remove all dependence on the RPC layer from autoserv (and its children).

This bug is about adding a client_version tag in the RPC calls to allow us to differentiate between different types of callers of the RPC layer and version them as we start making big changes to the RPC layer / callers to deprecate it.
This will also help us identify unexpected callers who may break due to the upcoming high churn in the RPC layer.