[v8] Ensure that the WindowsDesktopReady event is emitted (#14859)

Ensure that the WindowsDesktopReady event is emitted

When desktop access is enabled, the TeleportReady event will not
be emitted until the WindowsDesktopReadyEvent is emitted, and it
turns out we have *never* emitted a WindowsDesktopReadyEvent.

This is likely due to desktop access being copied from kube access
since the very beginning. The same issue was recently fixed for
kube access in #9418.

lib/service/desktop.go

@@ -246,6 +246,7 @@ func (process *TeleportProcess) initWindowsDesktopServiceRegistered(log *logrus.
 				"Windows desktop service %s:%s is starting on %v.",
 				teleport.Version, teleport.Gitref, listener.Addr())
 		}
+		process.BroadcastEvent(Event{Name: WindowsDesktopReady, Payload: nil})
 		err := srv.Serve(listener)
 		if err != nil {
 			if err == http.ErrServerClosed {