[TASK] Introduce Signals in IndexRecord- and MetaDataRepository

In order to allow custom code to act on changes in the FAL 
Layer the repositories now emit signals on create, update
and delete.

Releases: 6.2
Resolves: #52952
Change-Id: Ib42c1cb2aef199af3b4565560bdb2e094ac1cf06
Reviewed-on: https://review.typo3.org/24896
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter