add sync-upstream action

.github/workflows/sync-rebase.yml

@@ -0,0 +1,27 @@
+name: Sync and Rebase
+
+on:
+  schedule:
+    - cron: '0 0 * * *' # every day
+  workflow_dispatch: # on button click
+
+jobs:
+  sync:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Sync with upstream
+        run: |
+          git remote add upstream [email protected]:storybookjs/storybook.git
+          git fetch upstream
+          git merge upstream/master
+          git push
+      - name: Rebase creevey branch
+        run: |
+          git checkout creevey
+          git rebase master
+          git push --force