Add CI action to build and publish docker images

.github/workflows/build_docker.yaml

@@ -0,0 +1,37 @@
+name: Build Docker Image
+
+on:
+  release:
+    types: [published]
+
+jobs:
+
+  build:
+
+    # prereleases are not pushed to Docker Hub
+    if: ${{ !github.event.release.prerelease }}
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v4
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v7
+        with:
+          file: Dockerfile
+          context: .
+          push: true
+          tags: "lutraconsulting/mergin-db-sync:${{ github.event.release.tag_name }},lutraconsulting/mergin-db-sync:latest"
+          platforms: linux/amd64,linux/arm64