## 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!

ee/clickhouse/views/insights.py
return {
            "result": ClickhouseSessions().run(
                team=self.team, filter=SessionsFilter(request=request, data={"insight": INSIGHT_SESSIONS})
            )
        }
    @cached_function()
    def calculate_path(self, request: Request) -> Dict[str, Any]:
        team = self.team
        filter = PathFilter(request=request, data={"insight": INSIGHT_PATHS})
        resp = ClickhousePaths().run(filter=filter, team=team)
        return {"result": resp}
    @action(methods=["GET"], detail=False)
    def funnel(self, request: Request, *args: Any, **kwargs: Any) -> Response:
        response = self.calculate_funnel(request)
        return Response(response)
    @cached_function()
    def calculate_funnel(self, request: Request) -> Dict[str, Any]:
        team = self.team
        filter = Filter(request=request, data={"insight": INSIGHT_FUNNELS})
        return {"result": ClickhouseFunnel(team=team, filter=filter).run()}
    @cached_function()
    def calculate_retention(self, request: Request) -> Dict[str, Any]:
        team = self.team
        data = {}
        if not request.GET.get("date_from"):
            data.update({"date_from": "-11d"})
        filter = RetentionFilter(data=data, request=request)
        result = ClickhouseRetention().run(filter, team)
        return {"result": result}