## Bug description

We've had a user create a funnel with Korean characters and 17 steps, which causes this issue:
![image](https://user-images.githubusercontent.com/1727427/120301818-8c212a00-c2cd-11eb-8b00-7ba242e4a9ab.png)

## Expected behavior

We should send requests to api/insight/funnel using POST instead of GET.

## How to reproduce

1.
2.
3.

## Environment

- [ ] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: _please provide_

## Additional context



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

posthog/api/action.py
result = self.get_people(request)
        return Response(result)
    def get_people(self, request: request.Request) -> Union[Dict[str, Any], List]:
        team = self.team
        filter = Filter(request=request)
        entity = get_target_entity(request)
        events = filter_by_type(entity=entity, team=team, filter=filter)
        people = calculate_people(team=team, events=events, filter=filter)
        serialized_people = PersonSerializer(people, context={"request": request}, many=True).data
        current_url = request.get_full_path()
        next_url = paginated_result(serialized_people, request, filter.offset)
        if request.accepted_renderer.format == "csv":
            csvrenderers.CSVRenderer.header = ["Distinct ID", "Internal ID", "Email", "Name"]
            content = [
                {
                    "Name": person.get("properties", {}).get("name"),
                    "Distinct ID": person.get("distinct_ids", [""])[0],
                    "Internal ID": person["uuid"],
                    "Email": person.get("properties", {}).get("email"),
                }
                for person in serialized_people
            ]
            return content
        return {
            "results": [{"people": serialized_people, "count": len(serialized_people)}],
            "next": next_url,
            "previous": current_url[1:],
        }
def filter_by_type(entity: Entity, team: Team, filter: Filter) -> QuerySet: