Changes the auth failed label into an auth status label, and prints a
dot once every half second while authenticating.
Also reduces the post-auth-failed pause to 1 second; 2 seconds is longer
than it seems.
By default it'll look at your environment to try to figure out which
display manager is used in order to start a new session. We first try
the org.freedesktop.DisplayManager dbus interface, and if that fails,
inspect XDG_SESSION_DESKTOP to try to figure out which display manager
is running.
The user can also still specify the correct display manager, or a custom
command.
This includes an abortive attempt to do a gtk4 dialog (which I don't
think is possible, as gtk4 doesn't allow embedding toplevels anymore),
and an iced dialog, which I just never started writing.
