Create the linger file directly instead of using loginctl enable-linger,
which fails in containers where systemd-logind isn't fully functional.
The linger file at /var/lib/systemd/linger/<user> is what systemd checks
to persist user instances across logouts.

After creating the linger file, explicitly start user@<uid>.service to
boot the user's systemd instance immediately. This creates the D-Bus
session bus socket at /run/user/<uid>/bus, which is required for
systemctl --user to work. Without this, roles like pipewire that manage
user-scoped services fail with "Failed to connect to user scope bus".

This also refactors the user creation to simplify the logic and make the
user.id available for both cases of password or default_password

Co-Authored-By: Claude.ai

If no user_password is provided, the behavior remains the same, it uses
the default changeme password and requires to be changed for using sudo

If a user_password is provided, this hashed password will be used
instead of the default and doesn't require changing on first usage of
sudo

This allows the creation and persisting of the /run/user/UID/
directories required for gpg smart-card forwarding agent.