Custom 'feedback_hook_url' per notification

[msfilho]

Today we can only set a global 'feedback_hook_url'.

However our application today is totally multi-client. Our API url is different depending on the user associated with the client, inside the same app.

Today you have the 'notif_id' with send a unique string to identify the notification, but this require us to create a separate service on a global domain to filter the feedback and foward the to final service (on the client url, all the logic and connections do database and configs depends on the url subdomain attached to the client).

Please add a 'feedback_hook_url' parameter to the notification too.