webhook via ngrok not challenged - local setup

[AndreSoble]

When trying to test the webhook locally using ngrok no challenge is beeing send to the webhook endpoint.

Steps to reproduce the behavior:

1. docker-compose up locally
2. sign in etc.
3. start ngrok to forward a webhook call to a simple local webhook which should log the API path and body.
4. Add the webhook using the ngrok url

Expected behavior
Papercups should send the challenge to the webhook.