[TASK] Improve page permission copyFromParent tests and docs

A new feature has been added with #89917 to provide the
possibility that user/group informations and permissions
are used from parent page where the new page is created,
instead of eventually configured defaults through long
standing TSconfig options, or even fallback to current
signed in backend user/user group.

The patch extend the test cases to make more clear
how this new feature is intended to work and improves
the feature .rst file to show how it can be leveraged.

Resolves: #96091
Related: #89917
Releases: master
Change-Id: I5f4478229af69f1abda9aa9e95f1e620743d07ba
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72290


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>