curl --request GET \
  --url https://core.ravenna.ai/api/custom-fields/{id} \
  --header 'x-ravenna-api-token: <api-key>'

{
  "id": "<string>",
  "workspaceId": "<string>",
  "key": "<string>",
  "label": "<string>",
  "description": "<string>",
  "required": true,
  "system": true,
  "config": "<any>",
  "type": "TEXT",
  "options": [
    {
      "id": "<string>",
      "value": "<string>",
      "order": 123,
      "description": "<string>",
      "color": "<string>",
      "icon": "<string>",
      "customFieldId": "<string>",
      "createdAt": "<string>",
      "updatedAt": "<string>"
    }
  ],
  "createdAt": "<string>",
  "updatedAt": "<string>",
  "_count": {
    "requestTypeCustomField": 123
  }
}