CHW-4704 WebhookLimitReached

maximum of 5 webhooks per user; delete an existing webhook before creating a new one

Default message: maximum of 5 webhooks per user; delete an existing webhook before creating a new one
HTTP status: 400 (client)

Problem. POST /api/webhooks returned 400 without creating the webhook. Cause. Each user is capped at 5 webhooks to keep the dispatcher fan-out bounded. Fix. Delete an existing webhook via DELETE /api/webhooks/{id} before creating a new one. HTTP 400.