[TASK] Missing signals on adding folder

There are signals for most filestorage operations performed
in the ResourceStorage, but not for adding a folder.

This patch adds the two missing signals.

Resolves: #54964
Releases: 6.2
Change-Id: Ia7e3970ea278bf5e74856008afe53083e91f0649
Reviewed-on: https://review.typo3.org/26863
Reviewed-by: Stefan Neufeind
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf