[startkde] Reset systemd failed units on login

If a service has recently failed multiple times, systemd will (quite cleverly) not restart it. This includes DBus activation so is indepdent of the systemd boot.

If a service gets into a broken state on a previous session where ithas different environment variables and a different display server, we shouldn't treat it as failed for a new session.

This shouldn't be needed with the other recent fixes, but it seems like a good practice nevertheless.

Gnome are doing something similar: https://gitlab.gnome.org/GNOME/gnome-session/-/blob/master/gnome-session/main.c#L565