refactor: add an understanding of nullable for swagger gen

ApiDto/Responses/CampusDetailsResponse.cs

@@ -1,4 +1,6 @@
-namespace Mirea.Api.Dto.Responses;
+using System.ComponentModel.DataAnnotations;
+
+namespace Mirea.Api.Dto.Responses;
 
 /// <summary>
 /// Represents detailed information about a campus.
@@ -8,11 +10,13 @@ public class CampusDetailsResponse
     /// <summary>
     /// Gets or sets the unique identifier of the campus.
     /// </summary>
+    [Required]
     public int Id { get; set; }
 
     /// <summary>
     /// Gets or sets the code name of the campus.
     /// </summary>
+    [Required]
     public required string CodeName { get; set; }
 
     /// <summary>