feat: image url migration

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

WebApp/DTOs/EventDetailsDto.cs

@@ -11,6 +11,7 @@ public record class EventDetailsDto
     [Required] public string? OrganisationName { get; set; }
     [Required][StringLength(50)] public string Title { get; set; }
     [StringLength(500)] public string Description { get; set; }
+    public string? ImageURL { get; set; }
     [Required][StringLength(100)] public string Location { get; set; }
     [Required] public DateTime? EventDate { get; set; }
     //ICollection<EventSkill> EventSkills,