* add base class for Graphql APIs
* add GithubAuthV4Service + updates to GH token pool
* update github forks to use GithubAuthV4Service
* rename GithubAuthService to GithubAuthV3Service
This code isn't being run during tests, though let's fix that later as part of #2733. Specifically:
> However _the pool itself_ could be used all the time; there's not a big advantage in turning that off when it doesn't need to be used.
Fix#2728