[FA-4] Adds an event bus infrastructure, a RabbitMQ implementation and rewires existing mutations on NovelService to utilize it.

FictionArchive.Service.Shared/Services/EventBus/IIntegrationEventHandler.cs

@@ -0,0 +1,12 @@
+namespace FictionArchive.Service.Shared.Services.EventBus;
+
+public interface IIntegrationEventHandler<in TEvent> : IIntegrationEventHandler where TEvent : IntegrationEvent
+{
+    Task Handle(TEvent @event);
+    Task IIntegrationEventHandler.Handle(IntegrationEvent @event) => Handle((TEvent)@event);
+}
+
+public interface IIntegrationEventHandler
+{
+    Task Handle(IntegrationEvent @event);
+}