[FEATURE] Introduce Site Settings Editor

A new Site Settings editor has been introduced that allows to configure
per-site settings in `config/sites/*/settings.yaml`.

The new backend module `Site Management > Settings` provides an overview
of sites which offer configurable settings and makes them editable based
on Site Set provided Settings Definitions.

The editor shows a list of settings categories and respective settings.
It will persist all settings into `config/sites/*/settings.yaml`.
The module will only persist settings that deviate from the site-scoped
default value. That means it will only change the minimal difference to
the settings set defined by the active sets for the respective site.

The backend module is currently available for administrators only, but
will likely be extended to be made available for editors in future.

Anonymous (undefined) site settings – as supported since TYPO3 v10 –
will not be made editable, but will be preserved as-is when persisting
changes through the settings editor.

Resolves: #104794
Releases: main
Change-Id: I7eea8445b86b50efa498238daa3436f0940f4b78
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84342


Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>