Package galera-arbitrator-4 has to depend on adduser

Since Debian trixie, apt, a required package, doesn't depend simply on adduser but merely on "base-passwd (>= 3.6.1) | adduser". In a minimal environment adduser might not have been installed yet.

Pre-Depend on adduser to satisfy the preinst script.

Signed-off-by: Adel Belhouane bugs.a.b@free.fr