## 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!
posthog/models/feature_flag.py
hash_key = "%s.%s" % (key, distinct_id)
        hash_val = int(hashlib.sha1(hash_key.encode("utf-8")).hexdigest()[:15], 16)
        return hash_val / __LONG_SCALE__
    def get_analytics_metadata(self) -> Dict:
        filter_count: int = len(self.filters.get("properties", []),) if self.filters else 0
        return {
            "rollout_percentage": self.rollout_percentage,
            "has_filters": True if self.filters and self.filters.get("properties") else False,
            "filter_count": filter_count,
            "created_at": self.created_at,
        }
@receiver(models.signals.post_save, sender=FeatureFlag)
def feature_flag_created(sender, instance, created, raw, using, **kwargs):
    if instance.created_by:
        event_name: str = "feature flag created" if created else "feature flag updated"
        posthoganalytics.capture(
            instance.created_by.distinct_id, event_name, instance.get_analytics_metadata(),
        )