ci: create docker workflow

.github/workflows/release.yml

@@ -98,3 +98,19 @@ jobs:
       with:
         files: target/${{ matrix.target }}/release/rathole-${{ matrix.target }}.zip
         generate_release_notes: true
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: rapiz1/rathole:latest, rapiz1/rathole:${{ github.ref_name }}