software/fluentd: Add missing instance-output-schema.json

See merge request nexedi/slapos!1576

software/fluentd/instance-output-schema.json

+{
+  "$schema": "https://json-schema.org/draft/2019-09/schema",
+  "description": "Values returned by Fluentd instantiation",
+  "additionalProperties": false,
+  "properties": {},
+  "type": "object"
+}

software/fluentd/software.cfg.json

@@ -7,6 +7,7 @@
       "title": "Default",
       "description": "Fluentd",
       "request": "instance-input-schema.json",
+      "response": "instance-output-schema.json",
       "index": 0
     }
   }