service: Support connecting containers to tailscale network

roles/service/defaults/main.yaml

@@ -28,6 +28,9 @@ service_database_secret_target: "{{ service_database_type }}"
 service_postgres_image: docker.io/pgautoupgrade/pgautoupgrade
 service_postgres_tag: alpine
 service_redis: false
+service_tailscale: false
+service_tailscale_login_server: ""
+service_tailscale_apikey: ""
 
 service_additional_containers: []