[BUGFIX] Add proper comments in DefaultConfiguration options

Some descriptions of options in DefaultConfiguration are not visible in
the Install Tool. These are added and made sure to be rendered
in the Install Tool.

Resolves: #76333
Releases: master, 7.6
Change-Id: I87d90b7614d5c90a1d212d0a214ef26dc2d5fcfc
Reviewed-on: https://review.typo3.org/48341


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>