chore: add GitHub Actions script to build APK and upload it to artifacts

.github/workflows/build.yaml

@@ -0,0 +1,32 @@
+name: Build
+
+on: pull_request
+
+jobs:
+  build_android:
+    name: Android
+    environment: release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Java
+        uses: actions/setup-java@v3
+        with:
+          distribution: 'zulu'
+          java-version: '11'
+      - name: Setup Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          channel: 'stable'
+      - name: Add keystore
+        run: echo "${{ secrets.ANDROID_KEYSTORE }}" | base64 -d > android/localmaterialnotes_keystore.jks
+      - name: Add key properties
+        run: echo "${{ secrets.ANDROID_KEY_PROPERTIES }}" > android/key.properties
+      - name: Build app
+        run: flutter build apk --release
+      - name: Archive APK
+        uses: actions/upload-artifact@v3
+        with:
+          name: CPM
+          path: build/app/outputs/flutter-apk/app-release.apk