chore: Add monthly workflow to build `push` Docker image (#7146)

Co-authored-by: louislam <1336778+louislam@users.noreply.github.com>

.github/workflows/build-docker-push.yml

@@ -0,0 +1,49 @@
+name: Build Docker Push Image
+
+on:
+  schedule:
+    # Runs at 2:00 AM UTC on the 1st of every month
+    - cron: "0 2 1 * *"
+  workflow_dispatch: # Allow manual trigger
+
+permissions: {}
+
+jobs:
+  build-docker-push:
+    # Only run on the original repository, not on forks
+    if: github.repository == 'louislam/uptime-kuma'
+    runs-on: ubuntu-latest
+    timeout-minutes: 120
+    permissions:
+      contents: read
+
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with: { persist-credentials: false }
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@c7c53464625b32c7a7e944ae62b3e17d2b600130 # v3.7.0
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@988b5a0280414f521da01fcc63a27aeeb4b104db # v3.6.1
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Use Node.js 20
+        uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f # v6.1.0
+        with:
+          node-version: 20
+
+      - name: Set up Go
+        uses: actions/setup-go@d35c59abb061a4a6fb18e82ac0862c26744d6ab5 # v5.5.0
+
+      - name: Install cross-env
+        run: npm install -g cross-env
+
+      - name: Build and push Docker image
+        working-directory: extra/uptime-kuma-push
+        run: npm run build-docker