[BUGFIX] Correct the description for the cache:warmup command

Warmup for frontend caches is not immplemented by
TYPO3 core, but may be provided by third party extensions.
Adapt the cache:warmup command description that frontend
warmup may not be implemented/available.

Resolves: #95058
Releases: main, 11.5
Change-Id: Iab4634ac96b3061876d970f6c38a88b8687648fe
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74237


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>