feat(ci): add release apk build

.github/workflows/flutter-release.yml

@@ -0,0 +1,53 @@
+# Based on https://medium.com/flutter-community/automating-publishing-your-flutter-apps-to-google-play-using-github-actions-2f67ac582032
+
+name: Flutter release
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  release:
+    name: Test, build and release    runs-on: ubuntu-latest    steps:
+      - name: Checkout
+        uses: actions/checkout@v1
+      
+      - name: Setup Java
+        uses: actions/setup-java@v1
+        with:
+          java-version: '12.x'      - name: Setup Flutter
+        uses: subosito/flutter-action@v1
+        with:
+          channel: beta      - name: Flutter version
+        run: flutter --version
+
+      - name: Cache pub dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.FLUTTER_HOME }}/.pub-cache
+          key: ${{ runner.os }}-pub-${{ hashFiles('**/pubspec.lock') }}
+          restore-keys: ${{ runner.os }}-pub-
+
+      - name: Download pub dependencies
+        run: flutter pub get
+      
+      - name: Run build_runner
+        run: flutter pub run build_runner build --delete-conflicting-outputs
+
+      - name: Download Android keystore
+        id: android_keystore
+        uses: timheuer/base64-to-file@v1.0.3
+        with:
+          fileName: key.jks
+          encodedString: ${{ secrets.ANDROID_KEYSTORE_BASE64 }}
+
+      - name: Create key.properties
+        run: |
+          echo "storeFile=${{ steps.android_keystore.outputs.filePath }}" > android/key.properties
+          echo "storePassword=${{ secrets.ANDROID_KEYSTORE_PASSWORD }}" >> android/key.properties
+          echo "keyPassword=${{ secrets.ANDROID_KEY_PASSWORD }}" >> android/key.properties
+          echo "keyAlias=${{ secrets.ANDROID_KEY_ALIAS }}" >> android/key.properties
+
+      - name: Build Android App Bundle
+        run: flutter build appbundle
+