qtquick: Add example of custom tabBar

Will do some styling in a follow up

examples/qtquick/customtabbar/main.qml

@@ -0,0 +1,27 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2020-2022 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sergio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+import QtQuick 2.6
+import QtQuick.Controls 2.12
+import com.kdab.dockwidgets 2.0 as KDDW
+
+ApplicationWindow {
+    visible: true
+    width: 1000
+    height: 800
+
+    KDDW.DockingArea {
+        id: dockWidgetArea
+        anchors.fill: parent
+
+        uniqueName: "MyMainLayout"
+    }
+}