Feature: #98957 - Respect write-protected settings.php in Install Tool

Description

The Admin Tools > Settings backend module now informs a system maintainer if the system/settings.php file is write-protected.

This allows to make the settings file read-only after deployments.

Impact

An info box is rendered in the module and each submodule, informing the system maintainer that the system/settings.php file is write-protected. In that case, all input fields are disabled and the submit buttons are not available.