[BUGFIX] Fix type of additionalConfig in media viewhelper

Change the type from string to array.

Resolves: #84848
Releases: master, 8.7
Change-Id: I28071b1116b2c9b4fcdcc639c378b3b9c0503066
Reviewed-on: https://review.typo3.org/56789


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>