Add topics to the current group subscription.

        This is used by the group leader to ensure that it receives metadata
        updates for all topics that any member of the group is subscribed to.

        Arguments:
            topics (list of str): topics to add to the group subscription

def group_subscribe(self, topics):
        """Add topics to the current group subscription.

        This is used by the group leader to ensure that it receives metadata
        updates for all topics that any member of the group is subscribed to.

        Arguments:
            topics (list of str): topics to add to the group subscription
        """
        if self._user_assignment:
            raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
        self._group_subscription.update(topics)