Add Github App auth functionality

[patrickmarabeas]

No description provided.

[leostolyarov]

Hey @patrickmarabeas, are you planning to continue working on this PR?

[jspiro]

Desperately looking forward to this!

[highb]

This would help our organization not run into Github API rate limits. Would appreciate an update on what the direction is here.

[patrickmarabeas]

Yeah, sorry, it's been a busy start to the year and there was enough drift between the providers it wasn't a simple task. I've got this in the immediate backlog to work on.

If you need an immediate solution you can run my v4 POC provider side-by-side - https:/patrickmarabeas/terraform-provider-github-v4 (sorry, you'll need to read the source for readme).

NOTE: Not all resources are capable of being managed by a GH App.

Splitting resources across multiple state files is also a good way to both speed up run times and reduce the API requirements for any one run.

[patrickmarabeas]

Closing in favor of #753