switch github action workflow to if condition for docker build

.github/workflows/maven.yaml

@@ -36,3 +36,32 @@ jobs:
       - name: Build with Maven
         run: mvn -B package --file pom.xml -Dspring.profiles.active=test
 
+  docker:
+    name: Docker Build
+
+    runs-on: ubuntu-latest
+
+    if: github.ref == 'refs/heads/master' || startsWith(github.ref, 'refs/tags/')
+
+    steps:
+      - uses: actions/checkout@v1
+
+      - 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: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Set output
+        id: vars
+        run: echo ::set-output name=tag::${GITHUB_REF#refs/*/}
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: daspawnw/vault-crd:${{ steps.vars.outputs.tag }}