Restores .github/workflows/plugin-release.yaml to main branch.
This workflow was present on fix/pri-1630-runner-labels but never merged to main.
Contains:
- RELEASE_URL pointing to github.com (not git.farh.net)
- RELEASE_APP_ID and RELEASE_APP_PRIVATE_KEY secrets
- check-secrets job validating RELEASE_APP_ID
- GitHub App token generation via actions/create-github-app-token@v3
- GitHub release creation via softprops/action-gh-release@v2
- Version bump and PR creation steps
Ref: PRI-1692
Co-Authored-By: Paperclip <noreply@paperclip.ing>
