Ladybird: Add setting for page to open on new tab

Author: https://github.com/guerinoni
Commit: 17e9db4fa1
Pull-request: https://github.com/SerenityOS/serenity/pull/17116
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/AtkinsSJ

Ladybird/SettingsDialog.h

@@ -25,5 +25,6 @@ private:
     QFormLayout* m_layout;
     QPushButton* m_ok_button { nullptr };
     QLineEdit* m_homepage { nullptr };
+    QLineEdit* m_new_tab_page { nullptr };
     QMainWindow* m_window { nullptr };
 };