Missing fields in response from 'Get metadata instance on folder'

### Description of the issue

(from a box dev pjander)

the example response doesn't show that the actual metadata instance values are also present on top level of response like
```
{
"$id": "929bec9c-5efd-4413-a413-3091d6d5401c",
"$version": 0,
"$type": "appitems-metadata-extractor-4611c063-d200-4b8c-a055-2541c1670bff",
"$parent": "folder_14425881422",
"$typeVersion": 2,
"$template": "appitems-metadata-extractor",
"$scope": "enterprise_218243562",
"extractorCreatedAt": "2025-10-31T14:44:15.661Z",
"folders": "[{\"folderId\":14425831841}]",
"metadataFields": "[{\"instruction\":\"Extract this information\",\"isActive\":true,\"fieldId\":\"4cd7c606-93fa-4141-ab8f-15b58a8b7c5b\"},{\"isActive\":false,\"fieldId\":\"b55cc9bd-2793-4322-ae3c-b671c4d7243e\"}]",
"extractorUpdatedAt": "2025-10-31T14:44:15.661Z",
"extractorCreatedBy": "8681575240",
"isAutomaticExtractionEnabled": "false",
"extractorUpdatedBy": "8681575240",
"status": "inactive",
"metadataTemplateId": "80864874-8287-4afa-a65e-9829d7b1ac57",
"overwriteMetadataInstances": "OVERWRITE",
"isBootstrappingEnabled": "false",
"enterpriseId": "218243562",
"usePremiumAgent": "false",
"name": "GraphQL E2E Test Extractor - 9da234",
"$canEdit": true
}
```

### Current content

_No response_

### Expected content

_No response_

### Link to the documentation page

https://developer.box.com/reference/get-folders-id-metadata-id-id/