Feedback for “Webhooks”

Hi team, I would love to be able to set the webhook in the body of `POST /items/images`

I wouldn't mind if we first need to set all possible webhook values in the admin console, and only being able to use those values as the webhook url. Many thanks for taking this in consideration 
```
{
  "prompt": string,
  "ref": string | null,
  "webhook": string | null,
}
```