## 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/utils.py
labels_format = "%a. {day} %B"
    if interval == "hour" or interval == "minute":
        labels_format += ", %H:%M"
    return date.strftime(labels_format.format(day=date.day))
def absolute_uri(url: Optional[str] = None) -> str:
    """
    Returns an absolutely-formatted URL based on the `SITE_URL` config.
    """
    if not url:
        return settings.SITE_URL
    return urljoin(settings.SITE_URL.rstrip("/") + "/", url.lstrip("/"))
def get_previous_week(at: Optional[datetime.datetime] = None) -> Tuple[datetime.datetime, datetime.datetime]:
    """
    Returns a pair of datetimes, representing the start and end of the week preceding to the passed date's week.
    """
    if not at:
        at = timezone.now()
    period_end: datetime.datetime = datetime.datetime.combine(
        at - datetime.timedelta(timezone.now().weekday() + 1), datetime.time.max, tzinfo=pytz.UTC,
    )  
    period_start: datetime.datetime = datetime.datetime.combine(
        period_end - datetime.timedelta(6), datetime.time.min, tzinfo=pytz.UTC,
    )  
    return (period_start, period_end)
def relative_date_parse(input: str) -> datetime.datetime: