[TASK] Add remark about plugin grouping in SwitchableControllerAction RST

Resolves: #91091
Releases: master
Change-Id: I88c8c7c7119d7dae485eb6013ce05aaee42145d7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64213


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Richard Haeser <richard@maxserv.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Richard Haeser <richard@maxserv.com>