## Bug description

When calculating Trends results with an aggregated (e.g. single output, like big number) display type, WAU/MAU don't work. This is because we have an `ACTIVE_USERS_SQL` query for time series display types, but we don't have a version of this for aggregated display types. (See ZEN-1043.)

## How to reproduce

1. Create an insight with a single WAU or MAU series.
2. Switch display type to "Number".
3. Open the "Debug ClickHouse queries" modal from the command palette.
4. See `COUNT(*)` instead of `COUNT(DISTINCT person_id)`.

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posthog/queries/trends/trends_event_query.py
_entity: Entity
    _filter: Filter
    def __init__(self, entity: Entity, *args, **kwargs):
        self._entity = entity
        super().__init__(*args, **kwargs)
    def get_query(self) -> Tuple[str, Dict[str, Any]]:
        _fields = (
            f"{self.EVENT_TABLE_ALIAS}.timestamp as timestamp"
            + (
                " ".join(
                    f', {self.EVENT_TABLE_ALIAS}."{column_name}" as "{column_name}"'
                    for column_name in self._column_optimizer.event_columns_to_query
                )
            )
            + " ".join(
                [
                    ", "
                    + get_property_string_expr("events", property, f"'{property}'", "properties", table_alias="e")[0]
                    + f" as {property}"
                    for property in self._extra_event_properties
                ]
            )
            + (f", {self.DISTINCT_ID_TABLE_ALIAS}.person_id as person_id" if self._should_join_distinct_ids else "")
            + (
                f", {self.SESSION_TABLE_ALIAS}.session_duration as session_duration"