Add github action config.

.github/workflows/flutter_build.yml

@@ -0,0 +1,26 @@
+name: Flutter Build
+on:
+  push:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/setup-java@v1
+        with:
+          java-version: "12.x"
+      - uses: subosito/flutter-action@v1
+        with:
+          channel: "stable" # 'dev', 'alpha', default to: 'stable'
+      - run: flutter pub get
+      - run: echo $ENCODED_KEYSTORE | base64 -di > ${HOME}/keystore.jks
+      - run: echo 'export KEYSTORE=${HOME}/keystore.jks' >> $BASH_ENV
+      - run: dart tool/env.dart
+      - run: flutter build apk --split-per-abi  --obfuscate --split-debug-info=debug/
+      - run: flutter build appbundle  --obfuscate --split-debug-info=debug/
+      - uses: actions/upload-artifact@v1
+        with:
+          name: release-apk
+          path: build/app/outputs/