## 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/decorators.py
def parameterized_decorator(f: Callable):
        @wraps(f)
        def wrapper(*args, **kwargs) -> Dict[str, Union[List, datetime, bool, str]]:
            
            request: HttpRequest = args[1]
            team = cast(User, request.user).team
            filter = None
            if not team:
                return f(*args, **kwargs)
            filter = get_filter(request=request, team=team)
            cache_key = generate_cache_key("{}_{}".format(filter.toJSON(), team.pk))
            
            if not request.GET.get("refresh", False):
                cached_result = get_safe_cache(cache_key)
                if cached_result and cached_result.get("result"):
                    return {**cached_result, "is_cached": True}
            
            result = f(*args, **kwargs)
            
            if result is not None and not (isinstance(result.get("result"), dict) and result["result"].get("loading")):
                cache.set(
                    cache_key, {"result": result["result"], "last_refresh": now()}, TEMP_CACHE_RESULTS_TTL,
                )
                if filter:
                    dashboard_items = DashboardItem.objects.filter(team_id=team.pk, filters_hash=cache_key)
                    dashboard_items.update(last_refresh=now())
            return result
        return wrapper
    return parameterized_decorator