## 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/total_volume.py
start_of_week_fix=start_of_week_fix(filter.interval),
                    **content_sql_params,
                )
            elif entity.math in COUNT_PER_ACTOR_MATH_FUNCTIONS:
                
                
                content_sql = VOLUME_PER_ACTOR_SQL.format(
                    event_query=event_query,
                    start_of_week_fix=start_of_week_fix(filter.interval),
                    **content_sql_params,
                    aggregator="distinct_id" if team.aggregate_users_by_distinct_id else "person_id",
                )
            elif entity.math_property == "$session_duration":
                
                
                content_sql = SESSION_DURATION_SQL.format(
                    event_query=event_query, start_of_week_fix=start_of_week_fix(filter.interval), **content_sql_params
                )
            else:
                content_sql = VOLUME_SQL.format(
                    event_query=event_query, start_of_week_fix=start_of_week_fix(filter.interval), **content_sql_params
                )
            null_sql = NULL_SQL.format(
                trunc_func=trunc_func,
                interval_func=interval_func,
                start_of_week_fix=start_of_week_fix(filter.interval),
            )
            params["interval"] = filter.interval