ci: add a workflow that updates the gazelle manifest and pushes updates

.github/workflows/examples_build_file_generation.yaml

@@ -0,0 +1,30 @@
+---
+name: Update gazelle manifest
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+    paths:
+      - 'examples/build_file_generation/requirements*.txt'
+
+permissions:
+  pull-requests: write
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Update gazelle manifest
+        working-directory: examples/build_file_generation
+        run: |
+          bazel run //:gazelle_python_manifest.update
+      - name: Update gazelle manifest
+        working-directory: examples/build_file_generation
+        run: |
+          git add gazelle_python.yaml
+          git commit -m "chore: update gazelle_python.yaml"
+          git push -u origin HEAD