[FEATURE] Save current workspace in ReferenceIndex

To reduce queries to accordant relations saved in the reference
index, add the current workspace that is used. This information
will be used later during publishing nested record sets (e.g.
for Inline Relational Record Editing).

Resolves: #56977
Releases: 6.2
Change-Id: I92851e243581a525bb99fafc9ed656fd613eeb82
Reviewed-on: https://review.typo3.org/28472
Reviewed-by: Wouter Wolters
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader