Add Dockerfile, TrueNAS SCALE compose file and image publishing on release

.gitea/workflows/release.yml

@@ -37,3 +37,26 @@ jobs:
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN || secrets.GITHUB_TOKEN }}
         run: sh deploy/publish-release.sh "${GITHUB_REF_NAME}"
+
+      # Skipped when the repository variable PUBLISH_DOCKER is "false", or fails alone
+      # if this runner has no Docker: the release above is already published by then.
+      # Optional secret REGISTRY_TOKEN (and variable REGISTRY_USER): an access token
+      # with package write permission, for servers where the job token can't push.
+      - name: Build and push the container image
+        if: ${{ vars.PUBLISH_DOCKER != 'false' }}
+        env:
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN || secrets.GITHUB_TOKEN }}
+          REGISTRY_USER: ${{ vars.REGISTRY_USER || github.actor }}
+        run: |
+          host=${GITHUB_SERVER_URL#*://}
+          owner=$(echo "$GITHUB_REPOSITORY_OWNER" | tr 'A-Z' 'a-z')
+          image="$host/$owner/beach"
+          echo "$REGISTRY_TOKEN" | docker login "$host" -u "$REGISTRY_USER" --password-stdin
+          # a container-driver builder can build several architectures in one go
+          docker buildx create --name release --driver docker-container --use >/dev/null 2>&1 || docker buildx use release
+          tags="-t $image:$GITHUB_REF_NAME"
+          case "$GITHUB_REF_NAME" in
+            *-*) ;;                       # pre-releases (v1.0.0-rc1) don't move :latest
+            *) tags="$tags -t $image:latest" ;;
+          esac
+          docker buildx build --platform linux/amd64 $tags --push .