## 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/insight.py
filters = request.GET.dict()
        for key in filters:
            if key == "saved":
                if str_to_bool(request.GET["saved"]):
                    queryset = queryset.filter(Q(saved=True) | Q(dashboard__isnull=False))
                else:
                    queryset = queryset.filter(Q(saved=False))
            elif key == "user":
                queryset = queryset.filter(created_by=request.user)
            elif key == INSIGHT:
                queryset = queryset.filter(filters__insight=request.GET[INSIGHT])
        return queryset
    
    
    
    
    
    
    
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