[TASK] Use descriptions over placeholders in sys_file_storage

It is best practice to use permanently visible information to help to
fill out forms of any kind. In case of sys_file_storage the placeholder
is even partially cut off, so one can't read the whole text.

Resolves: #102150
Releases: main, 12.4
Change-Id: I8ad357470b4ff7a42454aba77c14cc8b6a532e8b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81416


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>