[TASK] Harden site settings save action

Apply an additional form token (send via POST)
for the site settings save action, additionally
to the get-based route token.

Releases: main
Resolves: #104951
Change-Id: I33beefbf15172274a593b0889583eaa7008ef874
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86081


Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>