[TASK] Minor Installer.php clean up

Split method setupGeneral() to two methods.

Resolves: #47872
Releases: 6.2

Change-Id: I802264188159f04bd0542efd6a719c0e6e1b6c25
Reviewed-on: https://review.typo3.org/20463
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Wouter Wolters
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn