feat: publish to pub workflow

Author: Jens Becker

.github/workflows/publish_to_pub.yml

@@ -0,0 +1,20 @@
+name: Publish to pub.dev
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: 'Checkout'
+        uses: actions/checkout@v2
+        
+      - name: '>> Dart package <<'
+        uses: k-paxian/dart-package-publisher@master
+        with:
+          accessToken: ${{ secrets.OAUTH_ACCESS_TOKEN }}
+          refreshToken: ${{ secrets.OAUTH_REFRESH_TOKEN }}
+          format: true