Set the rule for users wishing to join the room.

        Args:
            room_id(str): The room to set the rules for.
            join_rule(str): The chosen rule. One of: ["public", "knock",
                "invite", "private"]

def set_join_rule(self, room_id, join_rule):
        """Set the rule for users wishing to join the room.

        Args:
            room_id(str): The room to set the rules for.
            join_rule(str): The chosen rule. One of: ["public", "knock",
                "invite", "private"]
        """
        content = {
            "join_rule": join_rule
        }
        return self.send_state_event(room_id, "m.room.join_rules", content)