ci: build and deploy multi-architecture container images

This commit adds a GitHub action using `docker buildx` to build and push
a multi-architecture image to Docker hub.

Signed-off-by: Gabriel Duque <[email protected]>

.github/workflows/build-docker-images.yml

@@ -0,0 +1,72 @@
+name: Deploy multi-architecture Docker images for chartmuseum with buildx
+
+on:
+  schedule:
+    - cron: '0 0 * * *' # everyday at midnight UTC
+  pull_request:
+    branches: master
+  push:
+    branches: master
+    tags:
+      - v*
+
+jobs:
+  buildx:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Prepare
+        id: prepare
+        run: |
+          DOCKER_IMAGE=chartmuseum/chartmuseum
+          DOCKER_PLATFORMS=linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64,linux/386
+          VERSION=edge
+
+          if [[ $GITHUB_REF == refs/tags/* ]]; then
+            VERSION=${GITHUB_REF#refs/tags/v}
+          fi
+
+          if [ "${{ github.event_name }}" = "schedule" ]; then
+            VERSION=nightly
+          fi
+
+          TAGS="--tag ${DOCKER_IMAGE}:${VERSION} --tag ${DOCKER_IMAGE}:latest"
+
+          echo ::set-output name=docker_image::${DOCKER_IMAGE}
+          echo ::set-output name=version::${VERSION}
+          echo ::set-output name=buildx_args::--platform ${DOCKER_PLATFORMS} \
+            --build-arg revision=$(git rev-parse --short HEAD) \
+            ${TAGS} .
+      -
+        name: Set up Docker Buildx
+        uses: crazy-max/ghaction-docker-buildx@v3
+      -
+        name: Docker Buildx (build)
+        run: |
+          docker buildx build --no-cache --pull --output "type=image,push=false" ${{ steps.prepare.outputs.buildx_args }}
+      -
+        name: Docker Login
+        if: success() && github.event_name != 'pull_request'
+        env:
+          DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
+          DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
+        run: |
+          echo "${DOCKER_PASSWORD}" | docker login --username "${DOCKER_USERNAME}" --password-stdin
+      -
+        name: Docker Buildx (push)
+        if: success() && github.event_name != 'pull_request'
+        run: |
+          docker buildx build --output "type=image,push=true" ${{ steps.prepare.outputs.buildx_args }}
+      -
+        name: Docker Check Manifest
+        if: always() && github.event_name != 'pull_request'
+        run: |
+          docker run --rm mplatform/mquery ${{ steps.prepare.outputs.docker_image }}:${{ steps.prepare.outputs.version }}
+      -
+        name: Clear
+        if: always() && github.event_name != 'pull_request'
+        run: |
+          rm -f ${HOME}/.docker/config.json