Adds `file_filters` to the internal file filters.
        `file_filters` can be single object or iterable.

def add_file_filters(self, file_filters):
        """
        Adds `file_filters` to the internal file filters.
        `file_filters` can be single object or iterable.
        """
        file_filters = util.return_list(file_filters)
        self.file_filters.extend(file_filters)