Implement data source to retrieve GitHub apps

[gnarea]

Terraform Version

1.1.0

Expected Behavior

A data source to retrieve the node_id of a GitHub app, so that I can use it in the github_branch_protection resource.

Actual Behavior

There's no such data source. I have to manually query the GitHub API to get the node_id; e.g.: https://api.github.com/apps/github-actions

References

#615 (comment)

[g-chouzadjian]

I've had a crack here: #1268. Verified this works for public GitHub apps, however I'm getting 403's when attempting to retrieve private apps even my _provider uses the app installation auth method.

[patrickmarabeas]

Confirmed by GitHub that private Apps can only be queried by the App itself, and not others.

[kfcampbell]

Closing via #1268.