Plesk : 403 Forbidden after messing around with your Ubuntu/Debian or CentOS server

One of the many reasons why you have a 403 error on your website when using Plesk and tweaking your server (updates for exemple that can modify your Apache2 configuration, it happened to me when installing Landscape) might be that you need to add the APACHE_RUN_USER (usually www-data but make sure by looking for it into