Added two examples for modeling a subscription service: signal/slot
connection-based and bindable property-based. The examples are based
on the example from Fabian's Qt WS talk about the bindable properties.
Pick-to: 6.2
Task-number: QTBUG-97655
Change-Id: I0345913b8b6e5c40b8477e128d36483598bdfcaa
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
