Try multi-platform builds and push to ghcr.io

.github/workflows/test.yaml

@@ -51,3 +51,32 @@ jobs:
       - run: poetry install
       # Run tests
       - run: poetry run pytest
+  build-push:
+    runs-on: ubuntu-latest
+    needs: test
+    env:
+      # Variables found by default in Docker Hub builder
+      DOCKER_REGISTRY: ghcr.io
+      DOCKER_REPO: tecnativa/docker-socket-proxy
+    steps:
+      # Prepare
+      - uses: actions/checkout@v2
+      - uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      # Build and push
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm/v8,linux/arm64,linux/ppc64le,linux/s390x
+          push: true
+          tags: |
+            ${{ DOCKER_REGISTRY }}/${{ DOCKER_REPO }}