AccountsService is a bit weird, the automatic login flag adjusts a
config file in /etc/gdm/
This doesn't work for two reasons:
- SDDM (our Display Manager) obviously doesn't read this file
- AccountsService doesn't create the folder if it doesn't exist, so we
can't even use if we tried.
This patch adjusts UserManager to write /etc/sddm.conf directly. It's
not ideal, but I think it's the only option we have, certainly in the
short term.
BUG: 363058