loginctl: show a nicer error message when no session/seat is available

loginctl: show a nicer error message when no session/seat is available

When calling loginctl {seat,session}-status without arguments, show a nicer
error message in case there's no suitable session/seat attached to the calling
tty.

Before:
~# loginctl seat-status
Could not get properties: Unknown object '/org/freedesktop/login1/seat/auto'.
~# systemd-run -q -t loginctl seat-status
Could not get properties: Unknown object '/org/freedesktop/login1/seat/auto'.
~# systemd-run -q -t loginctl session-status
Could not get properties: Unknown object '/org/freedesktop/login1/session/auto'.

After:
~# build/loginctl seat-status
Failed to get path for seat 'auto': Session '1' has no seat.
~# systemd-run -q -t build/loginctl seat-status
Failed to get path for seat 'auto': Caller does not belong to any known session and doesn't own any suitable session.
~# systemd-run -q -t build/loginctl session-status
Failed to get path for session 'auto': Caller does not belong to any known session and doesn't own any suitable session.

Resolves: #25199