[TASK] Scale custom backend logo to fit into given div

The custom backend logo could break the layout if
not properly scaled.

This issue is fixed by setting max-width
and max-height for the image.

Resolves: #94778
Releases: master
Change-Id: I98221c721e8f9d7a7a648807ce31c0e9a00390a6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70397


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>