[TASK] Improve appearance of site configuration overview

Align columns within the table to ensure a consistent reading flow.
Position the content and buttons at the beginning of the column.
Also increase space between table and "Unassigned site
configurations" area.

Resolves: #99789
Releases: main
Change-Id: Ida72a151766ef139ed1dfae1e44ccb5d8d5756ce
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77662


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>