[DOCS] Document index change for xml sitemap

The documentation is updated to reflect that pages.no_index=1
also removes a page from the XML Sitemap.

Releases: main, 12.4
Resolves: #103259
Change-Id: Ifab520afad4afca29e7fa20bbc342e384a6d65b0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83186


Tested-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Chris Müller <typo3@krue.ml>