[BUGFIX] Enable treeConfig overriding by Page TSconfig

Add treeConfig to whitelist to allow overriding rootUid
as described in the documentation. Example:

TCEFORM.pages.categories.config.treeConfig.rootUid = 1

Resolves: #47040
Releases: 6.2, 6.1, 6.0, 4.7
Change-Id: Idd55593b063daa0be3c2943400f82617b0bf6218
Reviewed-on: https://review.typo3.org/25237
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind