## 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



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posthog/utils.py
import base64
import datetime
import datetime as dt
import gzip
import hashlib
import json
import os
import re
import shutil
import subprocess
import sys
import time
import uuid
from itertools import count
from typing import (
    Any,
    Dict,
    Generator,
    List,
    Mapping,