Get all comments of letter
        This will iterate over all pages until it gets all elements.
        So if the rate limit exceeded it will throw an Exception and you will get nothing

        :param letter_id: the letter id
        :return: list

def get_all_comments_of_letter(self, letter_id):
        """
        Get all comments of letter
        This will iterate over all pages until it gets all elements.
        So if the rate limit exceeded it will throw an Exception and you will get nothing

        :param letter_id: the letter id
        :return: list
        """
        return self._iterate_through_pages(
            get_function=self.get_comments_of_letter_per_page,
            resource=LETTER_COMMENTS,
            **{'letter_id': letter_id}
        )