[FA-10] Adds user service and authentication service

FictionArchive.Service.AuthenticationService/Models/Requests/UserRegisteredWebhookPayload.cs

@@ -0,0 +1,17 @@
+namespace FictionArchive.Service.AuthenticationService.Models.Requests;
+
+public class UserRegisteredWebhookPayload
+{
+    // The body of the notification message
+    public string Body { get; set; }
+    
+    public string OAuthProviderId { get; set; }
+    
+    public string InviterOAuthProviderId { get; set; }
+
+    // The email of the user that created the event
+    public string EventUserEmail { get; set; }
+
+    // The username of the user that created the event
+    public string EventUserUsername { get; set; }
+}