def hold_request(request_type, key, data=None):
    """Hold some data for moderator approval.

        :param request_type: A `RequestType` enum value.
        :param key: The key piece of request data being held.
        :param data: Additional optional data in the form of a dictionary that
            is associated with the held request.
        :return: A unique id for this held request.
        """
