[DOCS] Add chapter about available PSR-14 event in EXT:lowlevel

Resolves: #100898
Related: #99717
Releases: main, 12.4
Change-Id: I08012b6ef37687cb07b835233da947ff0ffcce6c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79420


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