Add game manager

Scripts/Main.cs

@@ -6,11 +6,15 @@ public partial class Main : Node
 {
    [Export]
    public Array<PackedScene> Levels;
+   [Export]
+   public PackedScene GameManager;
 
    public void LoadLevel(int indexToLoad)
    {
       var sceneToLoad = Levels.ElementAt(indexToLoad);
       CallDeferred(nameof(DeferredGoToScene), sceneToLoad);
+      var gameManager = GameManager.Instantiate();
+      AddChild(gameManager);
    }
 
    public void LoadNextLevel(int currentSceneIndex)