forage_select_data, go back to ForageWeb.ForageController module for more information.
Renders paginated data into a shape that the select widget expects.
This function returns a map. The user must use the JSON encoder in the Phoenix application to generate a JSON response.
It would be more succint to return JSON directly from this function, but Forage has no way of invoking the application's JSON encoder, so we leave that responsibility to the user.