[DOCS] Switch Reports documentation to PHP-based rendering

* Introduce a guides.xml, the presence of this file
  triggers the new rendering.
* Remove outdated genindex: not supported anymore
* Remove old Settings.cfg, was only used for Sphinx

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

Resolves: #103337
Releases: main, 12.4, 11.5
Change-Id: Ieb11f8a14c159953d0b6412b7cf2745f221ab788
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83351


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