## Bug description

Currently, decide endpoint takes 10+ seconds on kea.js.org.

This means that for first-time visitors autocapture nor session recording will be turned on for that long - losing valuable information.

When measuring this yesterday via shell ([slack thread](https://posthog.slack.com/archives/C0113360FFV/p1604951621008400)), the culprit was feature flags cohort checking. In this case, the cohort user was checked against was defined against the following action:

![Screenshot from 2020-11-10 11-41-32](https://user-images.githubusercontent.com/148820/98657215-49582e80-234a-11eb-9669-37d55e0d23bd.png)

Which currently looks through events of the data for that team.

## Expected behavior

Decide endpoint should use cached/materialized cohort ownership rather than calculating it on the fly.

## How to reproduce

1. Create an action with some selector
2. Create a cohort for has done action at any point
3. Create a feature flag using the cohort.
4. Measure /decide endpoint latency

## Environment

Cloud 

## Additional context

cc @EDsCODE who made it not time out by https://github.com/PostHog/posthog/pull/2299

#### *Thank you* for your bug report – we love squashing them!
ee/clickhouse/models/test/test_cohort.py
person1 = _create_person(
            distinct_ids=["some_other_id_2"],
            team_id=self.team.pk,
            properties={"$some_prop": "updated"},
            timestamp=datetime(2020, 1, 1, 12, 0, 1),
        )
        _create_person(
            uuid=person1.uuid,
            distinct_ids=["some_other_id"],
            team_id=self.team.pk,
            properties={"$some_prop": "something"},
            timestamp=datetime(2020, 1, 1, 12, 0, 4),
        )
        cohort1 = Cohort.objects.create(
            team=self.team, groups=[{"properties": {"$some_prop": "updated"}}], name="cohort1",
        )
        final_query, params = format_filter_query(cohort1)
        result = sync_execute(final_query, {**params, "team_id": self.team.pk})
        self.assertEqual(len(result), 0)