[TASK] Prepare selectSingle fields to use maxitems=1

To prevent using the renderType for checking whether
a column of SelectRelationFieldType is a single
reference, we set the maxitems option to 1. This
allows to keep existing functionality unmodified.

Resolves: #104424
Releases: main
Change-Id: I1190f6957e7351c79e23f2a313b3f4775ee130d0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85286


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Georg Ringer <georg.ringer@gmail.com>