michele: max lunghezza login

Models/Login.cs

@@ -1,13 +1,18 @@
-namespace VirtualTask.Models
+using System.ComponentModel.DataAnnotations;
+
+namespace VirtualTask.Models
 {
     public class Login
     {
+        [StringLength(20)]
         /// <summary>Username</summary>
         public string? Username { get; set; }
 
+        [StringLength(20)]
         /// <summary>Password</summary>
         public string? Password { get; set; }
 
+        [StringLength(5)]
         /// <summary>Tenant</summary>
         public string? Tenant { get; set; }
     }