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

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

@@ -0,0 +1,11 @@
+namespace FictionArchive.Service.Shared.Services.EventBus;
+
+public class SubscriptionManager
+{
+    public Dictionary<string, Type> Subscriptions { get; } = new Dictionary<string, Type>();
+
+    public void RegisterSubscription<TEvent>()
+    {
+        Subscriptions.Add(typeof(TEvent).Name, typeof(TEvent));
+    }
+}