## 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
steps = ActionStepSerializer(many=True, required=False)
    count = serializers.SerializerMethodField()
    created_by = UserBasicSerializer(read_only=True)
    class Meta:
        model = Action
        fields = [
            "id",
            "name",
            "post_to_slack",
            "slack_message_format",
            "steps",
            "created_at",
            "deleted",
            "count",
            "is_calculating",
            "last_calculated_at",
            "created_by",
            "team_id",
        ]
        extra_kwargs = {"team_id": {"read_only": True}}
    def get_count(self, action: Action) -> Optional[int]:
        if hasattr(action, "count"):
            return action.count  
        return None
    def _calculate_action(self, action: Action) -> None: