[BUGFIX] Show image metadata description

Show the description as a placeholder when an image
is added as a reference.

Resolves: #81235
Releases: master, 8.7
Change-Id: I75363f74ba72bf4fd95b2a2e9a2a061ad250f825
Reviewed-on: https://review.typo3.org/56438


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>