## Bug description

From [a customer report](https://posthoghelp.zendesk.com/agent/tickets/653):

```
I'm accessing insight results through the API, and I’ve noticed that sometimes the result is null in the response.
When I go and view the insight in Posthog and tap “refresh” the result starts to return in the API response.
I’ve also noticed there is a “refreshing” boolean flag in the insight response.
How do I set the insight to either refresh periodically or on request so I always get a result through the API?
```

It seems like the insight returns null if it's not refreshed manually from the frontend.

## How to reproduce

1. Call an insight with GET | /api/projects/:project_id/insights/:id
2. Response is `null`
3. Refresh the insight from the frontend
4. Response is populated

## Environment

- [ ] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: please provide

## Additional context


posthog/api/insight.py
return insight.get_effective_privilege_level(self.context["request"].user.id)
    def to_representation(self, instance: Insight):
        representation = super().to_representation(instance)
        dashboard: Optional[Dashboard] = self.context.get("dashboard")
        representation["filters"] = instance.dashboard_filters(dashboard=dashboard)
        if "insight" not in representation["filters"]:
            representation["filters"]["insight"] = "TRENDS"
        context_cache_key = self.context.get("filters_hash")
        representation["filters_hash"] = context_cache_key if context_cache_key is not None else instance.filters_hash
        return representation
class InsightViewSet(TaggedItemViewSetMixin, StructuredViewSetMixin, ForbidDestroyModel, viewsets.ModelViewSet):
    queryset = Insight.objects.all()
    serializer_class = InsightSerializer
    permission_classes = [IsAuthenticated, ProjectMembershipNecessaryPermissions, TeamMemberAccessPermission]
    throttle_classes = [PassThroughClickHouseBurstRateThrottle, PassThroughClickHouseSustainedRateThrottle]
    renderer_classes = tuple(api_settings.DEFAULT_RENDERER_CLASSES) + (csvrenderers.CSVRenderer,)
    filter_backends = [DjangoFilterBackend]
    filterset_fields = ["short_id", "created_by"]
    include_in_docs = True
    retention_query_class = Retention
    stickiness_query_class = Stickiness
    paths_query_class = Paths
    def get_serializer_class(self) -> Type[serializers.BaseSerializer]: