[BUGFIX] Extend label to clarify the role of "Media Extra" as BE module

Change-Id: Iff25e9e9ac02df0ebf77e70e20ad49a042611bd1
Releases: 3.0.0
Resolves: #55630
Reviewed-on: https://review.typo3.org/30440
Reviewed-by: Fabien Udriot
Tested-by: Fabien Udriot