Add displayname for the found guardian combobox

Models/Guardian.cs

@@ -15,5 +15,13 @@ namespace GreatHomeChildcare.Models
         public string EmailAddress { get; set; }
         public int PinNumber { get; set; }
         public int isAdmin { get; set; }
+
+        //readonly property to populate a single guardian's full name.
+        // this is a "Get" only property
+        public string DisplayName
+        {
+            get =>
+                $"{LastName}, {FirstName}";
+        }
     }
 }