Feature: #104069 - Improved backend notifications display and handling

Description

The notifications shown on the lower right now have a "Clear all" button to allow the user to clear all notifications with a single click. This button is only displayed when two or more notifications are on screen.

In case the height of the notification container exceeds the viewport, a scroll bar will allow the user to navigate through the notifications.

Impact

Handling of multiple notifications has been improved by allowing to scroll and clear all notifications at once.