## 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/test/test_insight.py
filter_dict = {
                "events": [{"id": "$pageview"}],
            }
            DashboardItem.objects.create(
                filters=Filter(data=filter_dict).to_dict(), team=self.team, short_id="12345678",
            )
            
            new_team = Team.objects.create(organization=self.organization)
            DashboardItem.objects.create(
                filters=Filter(data=filter_dict).to_dict(), team=new_team, short_id="12345678",
            )
            response = self.client.get("/api/insight/?short_id=12345678")
            self.assertEqual(response.status_code, status.HTTP_200_OK)
            self.assertEqual(len(response.json()["results"]), 1)
            self.assertEqual(response.json()["results"][0]["short_id"], "12345678")
            self.assertEqual(response.json()["results"][0]["filters"]["events"][0]["id"], "$pageview")
        def test_basic_results(self):