[TASK] Increase size of config field for backend_layout

Make textarea size of config field in backend_layout the same as
sys_template config field.

The config field is too small now, which results in a horizontal scrollbar.

Resolves: #72882
Releases: master
Change-Id: I95e35c24b8cf5f57e59bd14bf22e25c9984ad6d2
Reviewed-on: https://review.typo3.org/46139


Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>