## 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/action.py
calculate_action.delay(action_id=action.pk)
    def validate(self, attrs):
        instance = cast(Action, self.instance)
        exclude_args = {}
        if instance:
            include_args = {"team": instance.team}
            exclude_args = {"id": instance.pk}
        else:
            attrs["team_id"] = self.context["view"].team_id
            include_args = {"team_id": attrs["team_id"]}
        if Action.objects.filter(name=attrs["name"], deleted=False, **include_args).exclude(**exclude_args).exists():
            raise serializers.ValidationError(
                {"name": "This project already has an action with that name."}, code="unique"
            )
        return attrs
    def create(self, validated_data: Any) -> Any:
        steps = validated_data.pop("steps", [])
        validated_data["created_by"] = self.context["request"].user
        instance = super().create(validated_data)
        for step in steps:
            ActionStep.objects.create(
                action=instance, **{key: value for key, value in step.items() if key not in ("isNew", "selection")},
            )
        self._calculate_action(instance)
        posthoganalytics.capture(
            validated_data["created_by"].distinct_id, "action created", instance.get_analytics_metadata()
        )
        return instance
    def update(self, instance: Any, validated_data: Dict[str, Any]) -> Any: