[Bluez DBus Peripheral] Finishing Touches

(This task was originally a placeholder for collecting the miscellaneous tasks to complete the Bluez DBus peripheral backend support;
identified tasks that are not clearly part of just one of the other tasks under QTBUG-66909).

Now this task focuses on ensuring the right characteristic/descriptor properties wrt. to encryption, authorization, authentication and extended properties are covered to the extent they can be covered by Qt code. BlueZ DBus API is a high abstraction level API with regards to these, but it needs to be made sure that the expectations towards the application top (Qt) are met. This primarily means proper flag setting during the initial peripheral application registration, and possible DBus replies during application usage.