As a user, I want to be able to unsubscribe from a link

We need an endpoint accessible only via GET to be able to unsubscribe to a notification.

For instance, having a unsubscribe link at the end of an email is rally useful.

The user needs some feedbacks, when access this page:

• does my unsubscribe went well?
• does my url is fine and working?

Need some styling for the pages that will display feedback informations to the user.