Add presubmits for compositions.

- Add github action targetting experiments/**
- Add tests for jinja expander

.github/workflows/presubmit-compositions.yaml

@@ -0,0 +1,38 @@
+# Copyright 2023 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: presubmit-compositions
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    paths:
+      - "experiments/**"
+  push:
+    branches: ["master"]
+    paths:
+      - "experiments/**"
+jobs:
+  expander-jinja2:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@v4
+      - name: "verify expander-jinja2 in a kind cluster"
+        run: |
+          cd experiments/compositions/composition
+          make unit-test-expander-jinja2
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true