build(docker): auto docker push when pushing git tags (#258)

.github/workflows/docker.yaml

@@ -0,0 +1,30 @@
+name: Docker
+
+on:
+  push:
+    tags:
+      - v**
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v2
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v2
+    - name: Login to Docker Hub
+      uses: docker/login-action@v2
+      with:
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_TOKEN }}
+    - name: Build docker image
+      uses: docker/build-push-action@v2
+      with:
+        context: .
+        file: Dockerfile
+        # push: ${{ startsWith(github.ref, 'refs/tags/') }}
+        push: true
+        tags: scrolltech/l2geth:${{github.ref_name}}
+        # cache-from: type=gha,scope=${{ github.workflow }}
+        # cache-to: type=gha,scope=${{ github.workflow }}