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

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

@@ -0,0 +1,25 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace FictionArchive.Service.Shared.Services.EventBus;
+
+public class EventBusBuilder<TEventBus> where TEventBus : class, IEventBus
+{
+    private readonly IServiceCollection _services;
+    private readonly SubscriptionManager _subscriptionManager;
+
+    public EventBusBuilder(IServiceCollection services)
+    {
+        _services = services;
+        _services.AddSingleton<IEventBus, TEventBus>();
+        
+        _subscriptionManager = new SubscriptionManager();
+        _services.AddSingleton<SubscriptionManager>(_subscriptionManager);
+    }
+
+    public EventBusBuilder<TEventBus> Subscribe<TEvent, TEventHandler>() where TEvent : IntegrationEvent where TEventHandler : class, IIntegrationEventHandler<TEvent>
+    {
+        _services.AddKeyedTransient<IIntegrationEventHandler, TEventHandler>(typeof(TEvent).Name);
+        _subscriptionManager.RegisterSubscription<TEvent>();
+        return this;
+    }
+}