Add forgejo runner setup

templates/docker-compose.j2

@@ -43,3 +43,27 @@ services:
       - forgejo
     volumes:
       - {{ postgres_dir }}:/var/lib/postgresql/data
+
+  docker-in-docker:
+    image: docker:dind
+    privileged: true
+    container_name: 'docker_dind'
+    command: ['dockerd', '--host', 'tcp://0.0.0.0:2375', '--tls=false']
+    restart: 'unless-stopped'
+
+  # see https://forgejo.org/docs/latest/admin/runner-installation/#oci-image-installation
+  runner:
+    image: 'code.forgejo.org/forgejo/runner:3.4.1'
+    user: 1001:1001 # User without root privileges, but with access to {{ runner_dir }}
+    command: '/bin/sh -c "sleep 5; forgejo-runner daemon"'
+    environment:
+      DOCKER_HOST: tcp://docker-in-docker:2375
+    links:
+      - docker-in-docker
+    depends_on:
+      docker-in-docker:
+        condition: service_started
+
+    volumes:
+      - {{ runner_dir }}:/data
+    restart: 'unless-stopped'