[FEATURE] Display available commands in scheduler

The scheduler submodule "Available scheduler commands"
lists all registered scheduler commands.

This list is now grouped by the extension name to
improve readability.

Additionally, cli commands that can be executed as
scheduler commands are now listed as well.

Minor drive-by changes are applied along the way.

Resolves: #99436
Releases: main
Change-Id: I879a7fcc7b1593054958cbd4419c13ff1b4b7ff5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77239


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>