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