Add GitHub Action to generate Docker images

.github/workflows/docker.yml

+name: Docker
+on:
+  schedule:
+    - cron: '0 20 * * *'
+  push:
+    tags:
+      - '*.*.*'
+jobs:
+  multi:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./packaging/docker/Dockerfile
+          platforms: linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64
+          push: true