[CD] Added submodule update workflow.

.github/workflows/sync.yml

@@ -0,0 +1,24 @@
+name: Update submodules
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Pull & update submodules recursively
+        run: |
+          git submodule update --init --recursive
+          git submodule update --recursive --remote
+      - name: Commit & push changes
+        run: |
+          git config --global user.name GitHub
+          git config --global user.email actions@github.com
+          git commit -am "[dmitmel] Update submodule" | true
+          git push