curl --request GET \
  --url http://localhost:8080/menu-layout/available-callbacks

{
  "items": [
    {
      "callback_data": "<string>",
      "name": "<string>",
      "category": "<string>",
      "description": "<string>",
      "default_text": {},
      "default_icon": "<string>",
      "requires_subscription": false,
      "is_in_menu": false
    }
  ],
  "total": 123,
  "categories": [
    "<string>"
  ]
}