Auto-draft release notes by bot (#667)

.github/release-drafter.yml

+template: |
+  ## What's Changed
+
+  $CHANGES

.github/workflows/milestone.yml

-on: milestone
-name: On Milestone
-jobs:
-  createReleaseNotes:
-    name: Create Release Notes
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@master
-    - name: Create Release Notes
-      uses: mmornati/release-notes-generator-action@master
-      env:
-        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}