add github action for multiarch docker build

.github/workflows/image.yml

@@ -0,0 +1,30 @@
+name: build docker image
+
+on:
+  push:
+    branches:
+      - "!*"
+    tags:
+      - "v*"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the code
+        uses: actions/checkout@v2
+      - name: Install buildx
+        id: buildx
+        uses: crazy-max/ghaction-docker-buildx@v1
+        with:
+          version: latest
+      - name: Get latest release version number
+        id: get_version
+        uses: battila7/get-version-action@v2
+      - name: Login to Docker Hub
+        run: echo "${{ secrets.DOCKER_PASSWORD }}" | docker login -u "${{ secrets.DOCKER_USERNAME }}" --password-stdin
+      - name: Build multiarch image
+        run: |
+          docker buildx build --push \
+            --tag fradelg/mysql-cron-backup:{{ steps.get_version.outputs.version-without-v }} \
+            --platform linux/amd64,linux/arm/v7,linux/arm64 .