[DOCS] Switch sys_note documentation to PHP-based rendering

* Introduce a guides.xml, the presence of this file
  triggers the new rendering.
* Remove old Settings.cfg, was only used for Sphinx

Attention: Backport needs manual changes to the guides.xml.

This manual exists since TYPO3 v12

Resolves: #103333
Releases: main, 12.4
Change-Id: I6815646569ac3dd792156518633c6e5881342d90
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83324


Tested-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Lina Wolf <112@linawolf.de>
Tested-by: Lina Wolf <112@linawolf.de>
Tested-by: core-ci <typo3@b13.com>