Description of problem:

With the introduction of new idle sessions stopping of systemd (StopIdleSessionSec) it would be nice to see how long sessions are idle.

The command 'loginctl list-sessions' might be a good place to have it added.

~~~
[cb/Azure] root@li-lc-2635:~# loginctl
SESSION     UID USER                     SEAT TTY
     15 1170034 vrempet-admin      pts/0
     16 1170034 vrempet-admin      pts/1

2 sessions listed.
[cb/Azure] root@li-lc-2635:~#
~~~

Steps to Reproduce:
1. Execute below command 

 # loginctl

Actual results:

     SESSION     UID USER                     SEAT TTY
     15 1170034 vrempet-admin      pts/0
     16 1170034 vrempet-admin      pts/1

2 sessions listed.

Expected results:

Customer wants to see the idle time of current sessions.