feat: image url migration

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

WebApp/DTOs/EventCreateDto.cs

@@ -1,4 +1,4 @@
-using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations;
 using WebApp.Entities;
 
 namespace WebApp.DTOs;
@@ -8,6 +8,7 @@ public record class EventCreateDto
 (
     [Required][StringLength(50)] string Title,
     [StringLength(500)] string Description,
+    string? ImageURL,
     [Required][StringLength(100)] string Location,
     [Required] DateTime? EventDate,
     ICollection<EventSkill> EventSkills