feat: add reloader build action (#1041)

Signed-off-by: liubo02 <liubo02@pingcap.com>

Author: liubog2008

.github/workflows/reloader-dockerhub.yaml

@@ -0,0 +1,35 @@
+name: Build and Push Reloader Image
+
+on:
+  push:
+    tags:
+      - 'reloader/v*'
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USER }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+
+      - name: Extract image tag
+        id: vars
+        run: echo "image_tag=${GITHUB_REF_NAME#reloader/}" >> "$GITHUB_OUTPUT"
+
+      - name: Build and push image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: reload/Dockerfile_buildx
+          push: true
+          tags: pingcap/tidb-monitor-reloader:${{ steps.vars.outputs.image_tag }}