workflow: add github workflow for building extensions and upload

.github/workflows/extensions.yml

@@ -0,0 +1,34 @@
+name: Extension CI
+
+on:
+  workflow_dispatch:
+  push:
+    paths-ignore:
+      - README.md
+      - LICENSE
+      - .gitignore
+
+jobs:
+  build:
+    name: Build Extension
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v3
+        with:
+          java-version: 17
+          distribution: temurin
+
+      - name: Allow gradlew permission
+        run: chmod +x ./gradlew
+
+      - name: Build debug extension files
+        run: ./gradlew generateExtensions
+
+      - name: Upload extension files
+        uses: actions/upload-artifact@v3
+        with:
+          name: android-appstudio-extension-files
+          path: extension/build/extensions