Accessibility: make status notifications accessible (#15004)

* Accessibility: add aria-live to the notification component

react/features/notifications/components/web/Notification.tsx

 
     return (
         <div
+            aria-atomic = 'false'
+            aria-live = 'polite'
             className = { cx(classes.container, unmounting.get(uid ?? '') && 'unmount') }
             data-testid = { titleKey || descriptionKey }
             id = { uid }>