add github actions workflow to build docker images

.github/workflows/docker-images.yml

@@ -0,0 +1,77 @@
+name: docker-images
+
+on:
+  push:
+    branches: 
+    - master
+    - docker-test
+
+jobs:
+  multi:
+    strategy:
+      fail-fast: false
+      matrix:
+        image: 
+          - bandersnatch
+          - ftpsync
+          - homebrew-mirror
+          - nix-channels
+          - pub-mirror
+          - rustup-mirror
+        include:
+          - image: tunasync-scripts
+            dockerfile: .
+          - image: julia-mirror
+            dockerfile: dockerfiles/julia
+          - image: rubygems-mirror
+            dockerfile: dockerfiles/rubygems
+            
+    runs-on: ubuntu-latest
+    steps:
+      - 
+        name: Determin docker tag
+        env:
+          TAG_NAME: ${{ github.ref }}
+        run: |
+          if [ "${TAG_NAME##*/}" = "master" ]; then
+            tag=latest
+          else
+            tag=build-test
+          fi
+          echo "::set-env name=docker_tag::${tag}"
+      - 
+        name: Determin dockerfile
+        env:
+          DF: ${{ matrix.dockerfile }}
+          IMG: ${{ matrix.image }}
+        run: |
+          if [ -z "${DF}" ]; then
+            DF="dockerfiles/${IMG}"
+          fi
+          echo "::set-env name=docker_file::${DF}"
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: arm64
+      -
+        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: ${{ env.docker_file }}/Dockerfile
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: tunathu/${{ matrix.image }}:${{ env.docker_tag }}