[DOCS] ext:dashboard presets feature

The system extension ext:dashboard provides a way to register presets of
dashboards.
These presets can be configured via User TSconfig, if the user doesn't
have a dashboard yet.

Resolves: #91341
Releases: master
Change-Id: I174d6ee4a931bbe32f0cbed87db1545ee2785946
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64435


Tested-by: Richard Haeser <richard@maxserv.com>
Tested-by: Koen Wouters <koen.wouters@maxserv.com>
Tested-by: Daniel Siepmann <coding@daniel-siepmann.de>
Reviewed-by: Richard Haeser <richard@maxserv.com>
Reviewed-by: Koen Wouters <koen.wouters@maxserv.com>
Reviewed-by: Daniel Siepmann <coding@daniel-siepmann.de>