Only set Before=display-manager.service if it is actually present.
On headless systems, `systemctl list-units --state not-found` will
otherwise show display-manager.service.
Reported-In: https://github.com/NixOS/nixpkgs/issues/88597
This commit changes the console colors implementation
to use the kernel parameters instead of relying on terminal
escape sequences. This means the palette is applied by the
kernel itself with no custom code running in the initrd
and works for all virtual terminals (not only tty0).
This commit moves all the virtual console related options
to a dedicated config/console.nix NixOS module.
Currently most of these are defined in config/i18n.nix
with a "console" prefix like `i18n.consoleFont`,
`i18n.consoleColors` or under `boot` and are implemented
in tasks/kbd.nix.
Since they have little to do with actual internationalisation
and are (informally) in an attrset already, it makes sense to
move them to a specific module.
