Add workflow for creating release pull requests

Author: timreimherr

.github/workflows/create-release-pr.yml

@@ -0,0 +1,96 @@
+---
+# NOTE: This workflow belongs in the github/backup-utils repository.
+# It is stored here for convenience and should be copied to
+# github/backup-utils/.github/workflows/create-release-pr.yml
+#
+# This workflow is triggered via repository_dispatch from the
+# build-and-release workflow in backup-utils-private. It copies
+# docs and README.md from backup-utils-private onto a release branch
+# in backup-utils, then creates a PR using GITHUB_TOKEN so that the
+# PR author is github-actions[bot]. This allows the app token in
+# backup-utils-private to approve the PR as a different actor.
+name: Create Release PR
+
+on:
+  repository_dispatch:
+    types: [create-release-pr]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  create-release-pr:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ vars.RELEASE_CONTROLLER_APP_ID }}
+          private-key: ${{ secrets.RELEASE_CONTROLLER_APP_PRIVATE_KEY }}
+          owner: ${{ github.repository_owner }}
+          repositories: "backup-utils-private"
+
+      - name: Checkout backup-utils
+        uses: actions/checkout@v5
+
+      - name: Checkout backup-utils-private
+        uses: actions/checkout@v5
+        with:
+          token: ${{ steps.app-token.outputs.token }}
+          repository: github/backup-utils-private
+          path: './backup-utils-private'
+
+      - name: Replace docs directory with backup-utils-private docs
+        run: |
+          rm -rf docs
+          cp -r backup-utils-private/docs docs
+
+      - name: Replace README.md with backup-utils-private README.md
+        run: |
+          rm README.md
+          cp backup-utils-private/README.md README.md
+
+      - name: Delete backup-utils-private
+        run: |
+          rm -rf backup-utils-private
+
+      - name: Create release branch commit
+        run: |
+          version="${{ github.event.client_payload.version }}"
+          branch="release/$version"
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git checkout -B "$branch"
+          git add docs README.md
+          git commit --allow-empty -m "$version release"
+          git push --force-with-lease --set-upstream origin "$branch"
+
+      - name: Create or find release pull request
+        id: release-pr
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          version="${{ github.event.client_payload.version }}"
+          branch="release/$version"
+          pr_number="$(gh pr list --head "$branch" --base master --json number --jq '.[0].number')"
+
+          if [ -z "$pr_number" ]; then
+            pr_url="$(gh pr create \
+              --base master \
+              --head "$branch" \
+              --title "$version release" \
+              --body "Automated release PR for v$version.")"
+            pr_number="${pr_url##*/}"
+          fi
+
+          echo "number=$pr_number" >> "$GITHUB_OUTPUT"
+
+      - name: Enable auto-merge on release pull request
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr merge \
+            --squash \
+            --auto \
+            "${{ steps.release-pr.outputs.number }}"