[PUSH] Add support for Safari browser

Add support for Safari, as it's not using the standard VAPID protocol but it's own Apple protocol. https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/NotificationProgrammingGuideForWebsites/PushNotifications/PushNotifications.html#//apple_ref/doc/uid/TP40013225-CH3-SW9