Build and push docker images using GitHub Actions (#249)

Co-authored-by: Andrew Morgan <[email protected]>

.github/workflows/docker_push.yml

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+# GitHub actions workflow which builds and publishes the docker images.
+
+name: Build and push docker images
+
+on:
+  push:
+    tags: ["v*"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up QEMU
+        id: qemu
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: arm64
+
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Inspect builder
+        run: docker buildx inspect
+
+      - name: Log in to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_TOKEN }}
+
+      - name: Calculate docker image tags
+        id: set-tag
+        uses: docker/metadata-action@v3
+        with:
+          images: matrixdotorg/sygnal
+          tags: |
+            type=ref,event=tag
+
+      # we explicitly check out the repository (and use `context: .` in buildx)
+      # because we need to preserve the git metadata so that setuptools_scm
+      # (as part of Sygnal's setup.py) can deduce the package version.
+      # See: https://github.com/marketplace/actions/build-and-push-docker-images#path-context
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Build and push all platforms
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          labels: "gitsha1=${{ github.sha }}"
+          tags: "${{ steps.set-tag.outputs.tags }}"
+          file: "docker/Dockerfile"
+          platforms: linux/amd64,linux/arm64

changelog.d/249.docker

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+Automatically build the Docker image for each release and push it to Docker Hub using GitHub Actions.