First boot setup wizard and tuigreet integration

This MR is the first end-to-end try of implementing the new System Image V5 onboarding:

• Unless setup is completed, agetty autologins "root" (which has no pw anyway)
• The shell starts reform-setup in a special sway environment via a script in /etc/profile.d
• This sway is configured by the file /etc/reform-setup-sway-config
• greetd is installed (via Debian) and tuigreet binary dropped in /usr/bin
• Reform Setup Wizard writes /etc/greetd/config.toml with sway or wayfire preselected (users can change this in tuigreet or in this file)
• After successfuly completion, Reform Setup Wizard runs its cleanup.sh which 1. removes root autologin 2. removes itself from /etc/profile.d 3. enables and starts greetd