GitHub App Authentication

[fennifith]

We need to set up a GitHub App for PFP/hoof so that the backend can authenticate with the GH API independently and create its own commits in the playfulprogramming repo.

For authentication: See Generating a JSON Web Token (JWT) for a GitHub App and Authenticating as a GitHub App Installation

• Create a GitHub App for hoof
• Add secrets for the app credentials
• Install the app in playfulprogramming
• Obtain an auth token from the app for querying the API (and use it in client.ts - but keep GITHUB_TOKEN for local dev?)
  • Use GET /orgs/{org}/installation to obtain the installation ID
  • We'll need to refresh the auth token on any call if it expires, as it only lasts for 1 hour (this probably needs to be done in middleware)