Annotate result with aggregation result.

def annotate(self, **kwargs) -> "QuerySet":
        """
        Annotate result with aggregation result.
        """
        queryset = self._clone()
        for key, aggregation in kwargs.items():
            if not isinstance(aggregation, Aggregate):
                raise TypeError("value is expected to be Aggregate instance")
            queryset._annotations[key] = aggregation
            from tortoise.models import get_filters_for_field

            queryset._custom_filters.update(get_filters_for_field(key, None, key))
        return queryset