Add a Github Actions job to publish Docker images to Dockerhub and ghcr (#2027)

* Add a Github Actions job to publish Docker images to Dockerhub and ghcr
* Closes #1982

.github/workflows/docker-build.yml

@@ -0,0 +1,59 @@
+name: Docker build image on release
+
+# on:
+#   release:
+#     types: [published]
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    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: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      # -
+      #   name: Build and push
+      #   uses: docker/build-push-action@v2
+      #   with:
+      #     context: .
+      #     platforms: linux/amd64
+      #     push: true
+      #     tags: |
+      #       ctfd/ctfd:latest
+      #       ghcr.io/ctfd/ctfd:latest
+      #       ctfd/ctfd:${{ github.event.release.tag_name }}
+      #       ghcr.io/ctfd/ctfd:${{ github.event.release.tag_name }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          platforms: linux/amd64
+          push: true
+          tags: |
+            ctfd/ctfd:test-github-action
+            ghcr.io/ctfd/ctfd:test-github-action