add docker publish workflow

.github/workflows/docker-publish.yml

@@ -0,0 +1,88 @@
+name: Release Docker image to GHCR
+
+on:
+  # TODO: wire into release process
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Version to release'
+        required: true
+        default: 'latest'
+
+env:
+  REGISTRY: ghcr.io
+
+jobs:
+  build:
+    permissions:
+      contents: read
+      packages: write
+    strategy:
+      matrix:
+        runner:
+          - ubuntu-22.04-medium-arm64
+          - ubuntu-22.04
+    runs-on: ${{ matrix.runner }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          fetch-tags: true
+      - name: Log in to the Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Build and push image by digest
+        uses: docker/build-push-action@v6
+        id: build
+        with:
+          context: docker
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          labels: |
+            org.opencontainers.image.source=${{ github.repositoryUrl }}
+          outputs: type=image,name=${{ env.REGISTRY }}/${{ github.repository }},push-by-digest=true,name-canonical=true,push=true
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ runner.arch }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    runs-on: ubuntu-latest
+    needs: [build]
+    permissions:
+      packages: write
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+      - name: Log in to the Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create \
+            -t ${{ env.REGISTRY }}/${{ github.repository }}:${{ inputs.version }} \
+            $(printf '${{ env.REGISTRY }}/${{ github.repository }}@sha256:%s ' *)