adding new event for externalApp

Signed-off-by: Neil South <[email protected]>

Author: neildsouth

src/Messaging/Events/ExternalAppRequestEvent.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Monai.Deploy.Messaging.Events
+{
+    internal class ExternalAppRequestEvent
+    {
+    }
+}