CI: GitHub Action to automate license checks (#3)

* Add GHA to automate license checks

Author: eeaton

gcmvsp/.github/workflows/addlicense.yaml

@@ -0,0 +1,54 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+---
+name: addlicense
+
+on: # yamllint disable-line rule:truthy
+  pull_request: null
+
+permissions:
+  contents: read
+
+jobs:
+  addlicense:
+    permissions:
+      contents: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Pull container for addlicense
+        run: docker pull ghcr.io/google/addlicense:latest
+
+      - name: invoke addlicense
+        run: docker run -v "${PWD}":/src ghcr.io/google/addlicense -l "apache" -c "Google LLC" .
+
+      - name: Commit and push license fixes
+        # Run only on:
+        # - Pull requests
+        # - Not on the default branch
+        if: >
+          github.event_name == 'pull_request' &&
+          github.ref_name != github.event.repository.default_branch
+        uses: stefanzweifel/git-auto-commit-action@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          branch: ${{ github.event.pull_request.head.ref || github.head_ref || github.ref }}
+          commit_message: "chore: add license headers"
+          commit_user_name: addlicense
+          commit_user_email: no-reply@addlicense.dev