QML Live: document advanced techniques QML Live with an example

A major update of the description.

There are a few advanced techniques in QML Live which are still not documented. As a component on its own, QML Live currently provides a stand alone example with a Cluster app. This app will be used as a base to explain these techniques, since these techniques specific to QML Live itself and not to a code from other components.

The original scope of task to use the Parking app for this has been moved to AUTOSUITE-1296. This task will explain how to use QML Live with code from Neptune3 UI. The original plan to use the Parking app for this task is not feasible since it requires using qmake features from Neptune3 UI making QML Live dependent on another component.

It remains to be verified if this task with the corrected description will still be finished on time for 5.13.1 release.

PS. Even though there is a visual similarity, the Cluster app example is not the same as the Cluster app in the Neptune3 UI. The main difference is that this Cluster app runs stand alone and does not depend on other components from Qt Automotive Suite.