[FEATURE] Introduce Site Settings Read API

When using site configuration with
settings, they previously were accessible
via $site->getConfiguration()['settings'].

A site now also contains the settings
in a better way to read them via $site->getSettings()
where a SiteSettings object is resolved,
which contains all defined settings.

Settings can be defined in a settings.yaml
within the site configuration folder, which
are then read and populated along with
the site configuration.

The new SiteSettings Read API allows to access
the settings via a flat array or a full array.

Resolves: #99048
Releases: main
Change-Id: I07f1244d0ed45fe09d0f39dfdd52e8523a05b730
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76520


Tested-by: core-ci <typo3@b13.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Benni Mack <benni@typo3.org>