Update the AppHost eventing guide to cover the new `IDistributedApplicationEventingSubscriber` interface

[danegsta]

In 13.0, the old IDistributedApplicationLifecycleHook interface was deprecated and a new IDistributedApplicationEventingSubscriber interface was added as a replacement. We should update the eventing doc examples to use this new interface. We should either add a link to the migration example from the 13.0 What's New article (https://aspire.dev/whats-new/aspire-13/#migrating-from-lifecycle-hooks-to-events) or add a similar migration section for users upgrading from 9.x to 13.x.