✨ Add example of using Integration Events

[danielmackay]

We already have domain events in the template. We should also add an example of an 'integration event'.

• These integration events should be defined in Application
• They should not leak any of the Domain
• They should be fired AFTER DbContext.SavedChanges()
• Ideally these would be implemented via a SavedChangesInterceptor
• Could also add a mock service bus publisher

[danielmackay]

Sprint 5