add NotifyIcon NuGet package for tray icon support

windows/WinUI/packages.config

@@ -1,4 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="Hardcodet.NotifyIcon.Wpf" version="1.0.8" targetFramework="net45" />
   <package id="Newtonsoft.Json" version="9.0.1" targetFramework="net45" />
 </packages>