## 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)`.

#### *Thank you* for your bug report – we love squashing them!

posthog/queries/test/test_trends.py
test_person_ids = [  
            "016f70a4-1c68-0000-db29-61f63a926520",
            "016f70a4-1c68-0001-51a1-ad418c05e09f",
            "016f70a4-1c68-0002-9ea5-10186329258f",
            "016f70a4-1c68-0003-7680-697adb073c10",
            "016f70a4-1c68-0004-d0f8-7bd581c97eff",
            "016f70a4-1c68-0005-f593-e89d76db7a1f",
            "016f70a4-1c68-0006-bb84-d42937ef5989",
            "016f70a4-1c68-0007-923f-82720e97a6ba",
            "016f70a4-1c68-0008-8970-cbb33f01de1e",
            "016f70a4-1c68-0009-75a2-3755450b0b17",
        ]
        with freeze_time("2020-01-04T13:00:01Z"):
            all_distinct_ids = []
            for i, person_id in enumerate(test_person_ids):
                distinct_id = f"blabla_{i}"
                
                _create_event(
                    team=self.team,
                    event="sign up",
                    distinct_id=distinct_id,
                    properties={"$some_property": "value", "$bool_prop": True},
                    person_id=person_id,  
                )
                all_distinct_ids.append(distinct_id)
            person = _create_person(
                team_id=self.team.pk,
                distinct_ids=all_distinct_ids,