Add docs for switching to a non-root installation
This change adds a new chapter in the "Installation" section, explaining how to switch an existing "root installation" to a "non-root installation".
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The third breaking change window begins 2024-05-06 09:00 UTC and ends 2024-05-08 22:00 UTC.
This change adds a new chapter in the "Installation" section, explaining how to switch an existing "root installation" to a "non-root installation".