[DOCS] Remove confusing "cron command" ambiguity.

Remove the ambiguity of “cron command” that causes confusion for a
first time reader, as happened in https://forge.typo3.org/issues/75802.
Saying “cron command” implies the entire instruction, including the
shell command portion. Instead, we want only the patterns of the first
five fields of a crontab entry input file line, described in “The Open
Group Base Specifications Issue 7, 2018 edition” at
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/crontab.html.
There is no definitive name for these five fields as a group: “cron
schedule expression” or “crontab schedule expression” are
descriptive.

Releases: master
Resolves: #89632
Change-Id: I52c20b6a4b2fdb626687a5429d0a79503f92e1b8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62271


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Daniel Siepmann <coding@daniel-siepmann.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Daniel Siepmann <coding@daniel-siepmann.de>