feat(onboarding): dotnet snippet

frontend/src/component/onboarding/snippets/dotnet.md

@@ -7,14 +7,34 @@ dotnet add package Newtonsoft.Json
 
 2\. Initialize Unleash
 ```csharp
+using System;
 using Unleash;
+using Unleash.ClientFactory;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+public class Program
+{
+    public static async Task Main()
+    {
         var settings = new UnleashSettings()
         {
-    AppName = "unleash-onboarding-dotnet",
+            AppName = "codesandbox-csharp",
             UnleashApi = new Uri("<YOUR_API_URL>"),
+            SendMetricsInterval = TimeSpan.FromSeconds(1),
             CustomHttpHeaders = new Dictionary<string, string>()
             {
                 {"Authorization", "<YOUR_API_TOKEN>"}
             }
         };
+
+        var unleash =  new DefaultUnleash(settings);
+        var flag = "example-flag";
+
+        while (true) {
+            Console.WriteLine($"'{flag}' is enabled: {unleash.IsEnabled(flag)}");
+            await Task.Delay(1000);
+        }
+    }
+}
 ```