Allow optional for alternative login id determination

#android
#rb Pete.Procopio



#ROBOMERGE-SOURCE: CL 8376640 via CL 8376641 via CL 8376642 via CL 8377377 via CL 8380717
#ROBOMERGE-BOT: (v402-8361577)

[CL 8380781 by chris babcock in Main branch]

Engine/Build/Android/Java/src/com/epicgames/ue4/GameActivity.java.template

@@ -4057,6 +4057,8 @@ public class GameActivity extends $${gameActivitySuperClass}$$ implements Surfac
 	{
 		String loginId = null;
 
+	//$${gameActivityGetLoginIdAdditions}$$
+
 		// check for existing GUID fallback in internal
 		File file = new File(InternalFilesDir + "login-identifier.txt");
 		if (file.exists())