## 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
"""
    Grabs an email address and returns it masked in a human-friendly way to protect PII.
        Example: testemail@posthog.com -> t********l@posthog.com
    """
    index = email_address.find("@")
    if index == -1:
        raise ValueError("Please provide a valid email address.")
    if index == 1:
        
        return f"*{email_address[index:]}"
    return f"{email_address[0]}{'*' * (index - 2)}{email_address[index-1:]}"
def is_valid_regex(value: Any) -> bool:
    try:
        re.compile(value)
        return True
    except re.error:
        return False
def get_absolute_path(to: str) -> str:
    """
    Returns an absolute path in the FS based on posthog/posthog (back-end root folder)
    """
    return os.path.join(__location__, to)
class GenericEmails:
    """
    List of generic emails that we don't want to use to filter out test accounts.
    """
    def __init__(self):
        with open(get_absolute_path("helpers/generic_emails.txt"), "r") as f:
            self.emails = {x.rstrip(): True for x in f}
    def is_generic(self, email: str) -> bool: