ci: Added build-multiarch.yml to align merges

.github/workflows/build-multiarch.yml

@@ -0,0 +1,77 @@
+name: Build and publish multiarch
+on:
+  push:
+    branches:
+      - multiarch
+      - multiarch-latest
+      - test/multiarch/*
+    tags:
+      - "[0-9]+.[0-9]+.[0-9]+-multiarch"
+      - "[0-9]+.[0-9]+.[0-9]+-multiarch-latest"
+
+jobs:
+  docker-buildx:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2.2.0
+
+      - name: Prepare
+        id: prep
+        run: |
+          DOCKER_IMAGE=itzg/minecraft-server
+          VERSION=edge
+          if [[ $GITHUB_REF == refs/tags/* ]]; then
+            VERSION=${GITHUB_REF#refs/tags/}
+          fi
+          if [[ $GITHUB_REF == refs/heads/* ]]; then
+            VERSION=${GITHUB_REF#refs/heads/}
+            if [[ $VERSION == master ]]; then
+              VERSION=latest
+            fi
+          fi
+          TAGS="${DOCKER_IMAGE}:${VERSION//\//-}"
+          echo ::set-output name=tags::${TAGS}
+          echo ::set-output name=cache_from::${TAGS}
+          echo ::set-output name=version::${VERSION//\//-}
+          echo ::set-output name=cache_version::${VERSION//\//-}
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Cache Docker layers
+        uses: actions/cache@v2
+        with:
+          path: /tmp/.buildx-cache
+          key: ${{ runner.os }}-buildx-${{ steps.prep.outputs.cache_version }}-${{ github.sha }}
+          restore-keys: |
+            ${{ runner.os }}-buildx-${{ steps.prep.outputs.cache_version }}-
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: linux/amd64,linux/arm/v7,linux/arm64
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.prep.outputs.tags }}
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache
+          labels: |
+            org.opencontainers.image.documentation=https://github.com/itzg/docker-minecraft-server
+            org.opencontainers.image.source=https://github.com/itzg/docker-minecraft-server
+            org.opencontainers.image.version=${{ steps.prep.outputs.version }}
+            org.opencontainers.image.revision=${{ github.sha }}
+
+      - name: Image digest
+        run: echo ${{ steps.docker_build.outputs.digest }}