## 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
with freeze_time("2012-01-14T03:21:34.000Z"):
                for i in range(25):
                    event_factory(
                        team=self.team, event="$pageview", distinct_id="1", properties={"$some_property": f"value{i}"},
                    )
            with freeze_time("2012-01-15T04:01:34.000Z"):
                response = self.client.get(
                    "/api/insight/trend/",
                    data={
                        "events": json.dumps([{"id": "$pageview"}]),
                        "breakdown": "$some_property",
                        "breakdown_type": "event",
                    },
                )
            self.assertEqual(response.status_code, status.HTTP_200_OK)
            self.assertIn("offset=20", response.json()["next"])
        def test_insight_paths_basic(self):
            person_factory(team=self.team, distinct_ids=["person_1"])
            event_factory(
                properties={"$current_url": "/"}, distinct_id="person_1", event="$pageview", team=self.team,
            )
            event_factory(
                properties={"$current_url": "/about"}, distinct_id="person_1", event="$pageview", team=self.team,
            )
            response = self.client.get("/api/insight/path",).json()
            self.assertEqual(len(response["result"]), 1)
        
        if not is_clickhouse_enabled():
            @override_settings(CELERY_TASK_ALWAYS_EAGER=True)
            def test_insight_funnels_basic(self):