[TASK] EXT:Scheduler: Update documentation

Replaced images with new ones from current master.
Adjust the description text where necessary.
Change presentation of the "class not found" group.

Resolves: #72628
Releases: master
Change-Id: Icf6845c72b34afbf0105aa844e321a18878f16dd
Reviewed-on: https://review.typo3.org/55077


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>