fix: offload building DTOs to GUHF

DTO building allows for fully returning correct event's
skills and registrations

WebApp/DTOs/EventRegistrationDto.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+using WebApp.Entities;
+
+namespace WebApp.DTOs;
+
+public record class EventRegistrationDto
+{
+    public int EventId { get; set; }
+    public int UserId { get; set; }
+    public string UserName { get; set; }
+    public DateTime RegisteredAt { get; set; }
+
+    public EventRegistrationDto() { }
+
+};