Publish Docker image to GitHub registry

.github/workflows/docker.yml

@@ -0,0 +1,64 @@
+name: Publish Docker image
+
+on:
+  push:
+    branches:
+      - master
+  release:
+    types: [published]
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          tags: |
+            type=ref,event=branch,enable=true
+            type=ref,event=tag,enable=true
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v6
+        with:
+          push: true
+          # Set 'provenance: false' so there won't be a build for an unknown
+          # architecture (https://github.com/docker/build-push-action/issues/820)
+          # and calling delete-package-versions below will not result in an
+          # 'manifest unknown' error (https://github.com/actions/delete-package-versions/issues/90)
+          provenance: false
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=registry,ref=ghcr.io/${{ github.repository }}:latest
+          cache-to: type=inline
+
+      - name: Remove untagged container images
+        uses: actions/delete-package-versions@v5
+        with:
+          package-name: schwarzwald
+          package-type: container
+          delete-only-untagged-versions: true
+          min-versions-to-keep: 0