Allow to pass an Observable as notification content

[AndreKoepke]

It would be cool, when we can pass Observables as content for notifications. Then can something like this possible:

notificationService.show(translationService.stream('translationKey'));

Relates to:

scion-workbench/projects/scion/workbench-client/src/lib/notification/workbench-notification.config.ts

Line 37 in f9378e0

content?: any;

scion-workbench/projects/scion/workbench-client/src/lib/notification/workbench-notification-service.ts

Line 59 in f9378e0

public async show(notification: string | WorkbenchNotificationConfig, qualifier?: Qualifier): Promise<void> {