Subscribe and listen to Web Push Notifications through Angular Service Worker.
class SwPush { readonly messages: Observable<object>; readonly notificationClicks: Observable<{ action: string; notification: NotificationOptions & { title: string; }; }>; readonly subscription: Observable<PushSubscription>; readonly isEnabled: boolean; requestSubscription(options: { serverPublicKey: string; }): Promise<PushSubscription>; unsubscribe(): Promise<void>;}