Add release and mergeback workflows

This commit ensures that the changelog is updated before a release with
the correct date and version.

Also, after a release, a mergeback PR is created to ensure that the
changelog update and version bump is available in main.

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

@@ -22,12 +22,17 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: 3.5
+        python-version: 3.8
 
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
         pip install PyGithub==1.51 requests
 
+    - name: Update git config
+      run: |
+        git config --global user.email "github-actions@github.com"
+        git config --global user.name "github-actions[bot]"
+
     - name: Update release branch
       run: python .github/update-release-branch.py ${{ secrets.GITHUB_TOKEN }} ${{ github.repository }}