feat: image url migration

registrations can now store image urls, which will be shown at view.html

WebApp/Entities/Event.cs

@@ -1,4 +1,4 @@
-namespace WebApp.Entities
+namespace WebApp.Entities
 {
     public class Event
     {
@@ -6,6 +6,7 @@
         public int OrganisationId { get; set; }
         public required string Title { get; set; }
         public string? Description { get; set; }
+        public string? ImageURL { get; set; }
         public required string Location { get; set; }
         public required DateTime EventDate { get; set; }