extsvc/github: use injected log.Logger in v3 client
Created by: bobheadxi
This PR migrates GitHub v3 clients to use inject loggers. This allows users to provide a scope to identify which part of the codebase is using a particular client to make logging output more useful and more easily identify where API requests and API logs might be coming from.
This PR is also intended to serve as a reference migration for delegating further migrations to GitStart, e.g. https://github.com/sourcegraph/sourcegraph/issues/35514
Test plan
sg start
sg start dotcom
and tests pass