Improve NavigationService for automatic ObservableRecipient activation

[LeftTwixWand]

Issue #28 describes how to use CommunityToolkit.Mvvm.Messaging for ViewModels communication. The only one problem here, is every ViewModel which listens for a message, has to be manually activated: IsActive = true; to start listening.
So, it would be good to automatically activate such ViewModels somewhere in the NavigationService.
As a bad solution - all the ObservableRecipient instances can be activated in the Autofac container callback after they've being resolved.