[TASK] Display max file size hint

When configuring a form with a file size validator it can be helpful to
know what the servers' max upload capabilities are. As it may make sense
to set bigger values and then contact a server admin to adjust the
server settings, we do not want to restrict the input field. Instead,
a hint with the current configuration has been added to inform the
editor / integrator of the current limitations.

Resolves: #88055
Releases: master
Change-Id: Iaae73f8df87f47484e29a810c7531a117e35a286
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60595


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Dominik Merkel <merkel.dominik@googlemail.com>
Tested-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>
Reviewed-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>