MonitorOverlay and CenterConsoleWindow require documentation

In the System UI documentation, for Neptune, we talk about the following:

• ApplicationCCWindow (https://doc-snapshots.qt.io/neptune3ui/qml-applicationccwindow.html)
• ApplicationICWindow (https://doc-snapshots.qt.io/neptune3ui/qml-applicationicwindow.html)

But we are missing some pieces of information like:

• MonitorOverlay, which is a component based on QtApplicationManager's FrameTimer for the window and can be placed over any WindowObject in Neptune.
• SystemInfo Plugin that is used by the CenterConsoleWindow to fill model data inside the extension of MonitorOverlay (CenterConsoleMonitorOverlay) - to show CPU and memory consumption.

Since the goal of Neptune 3 UI is to show best practices to developers who have to implement an IVI system, it's necessary, I feel, that we document these missing pieces of information. That way we can link to this information when needed.