chore: add action to automate creation of release branches/prs (#3427)

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

@@ -0,0 +1,68 @@
+name: "Create Release PR"
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: New release version (e.g. 0.46.0)
+        type: string
+        required: true
+      target_branch:
+        description: Target branch to create a release/PR to
+        type: string
+        required: true
+        default: master
+
+jobs:
+  create-release-pr:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+        with:
+          fetch-depth: 0
+          token: "${{ secrets.RENKUBOT_GITHUB_TOKEN }}"
+          ref: '${{ github.event.inputs.target_branch}}'
+      - name: Setup Git
+        run: |
+          git config --global --add user.name "Renku Bot"
+          git config --global --add user.email "[email protected]"
+          git config push.autoSetupRemote true
+      - name: Create Branch
+        run: git checkout -b "release-${{ github.event.inputs.version }}"
+      - name: Update changelog
+        id: changelog
+        shell: bash
+        run: |
+          VERSION_LENGTH=$(echo -n "${{ github.event.inputs.version }}" | wc -m)
+          DELIMITER=$(printf "%.0s-" $(seq $VERSION_LENGTH))
+          sed -i -E "s/^(.*.. _changelog:)/\1\n\n${{ github.event.inputs.version }}\n$DELIMITER\n\n/" CHANGELOG.rst
+          head -n 10 CHANGELOG.rst
+      - name: Commit changes
+        run: |
+          git add CHANGELOG.rst
+          git commit -m "chore: create release ${{ github.event.inputs.version }}"
+          git push
+      - name: Create Pull Request
+        uses: actions/github-script@v6
+        with:
+          token: ${{ secrets.RENKUBOT_GITHUB_TOKEN }}
+          script: |
+            const { repo, owner } = context.repo;
+            const result = await github.rest.pulls.create({
+              title: 'release ${{ github.event.inputs.version }}',
+              owner,
+              repo,
+              head: 'release-${{ github.event.inputs.version }}',
+              base: '${{ github.event.inputs.target_branch }}',
+              body: [
+                '/deploy ',
+                'This PR is auto-generated by',
+                '[actions/github-script](https://github.com/actions/github-script).'
+              ].join('\n')
+            });
+            github.rest.issues.addLabels({
+              owner,
+              repo,
+              issue_number: result.data.number,
+              labels: ['release']
+            });
+