feat: allow enabling/disabling immutable releases for repos

[eliashaeussler]

Provides support for GitHub's Immutable Releases feature.

Example config:

# .github/settings.yml

repository:
  enable_immutable_releases: true

[vercel]

@eliashaeussler is attempting to deploy a commit to the Repository Settings Team on Vercel.

A member of the Team first needs to authorize it.