def files
      result = form.select_files.map { |label, id| { id: id, text: label } }
      render json: result
    end
def files
      result = form.select_files.map { |label, id| { id: id, text: label } }
      render json: result
    end
Renders a JSON response with a list of files in this admin set.
 This is used by the edit form to populate the thumbnail_id dropdown