[Hosts]Duplicate check improvements (#32805)

* moved duplicate check in a dedicate service and made it async

* addressed feedback

src/modules/Hosts/HostsUILib/Helpers/IDuplicateService.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using HostsUILib.Models;
+
+namespace HostsUILib.Helpers
+{
+    public interface IDuplicateService
+    {
+        void Initialize(IList<Entry> entries);
+
+        void CheckDuplicates(string address, string[] hosts);
+    }
+}