main/playerctl: add user service, adopt

[ttyyls]

Description

quoting the manpage

     Playerctl also comes with a daemon called playerctld which keeps track of
     media player activity. When playerctld is running, playerctl commands
     will act on the media player with the most recent activity.  Run the
     command playerctld daemon to start the daemon.

on systemd based distributions the dbus activation is tied to $DISPLAY, although
I don't see why not set it at a login.target since mpris is still usable and
thus potentially controllable on non-graphical environments.

regardless, the service depends on graphical.target and dbus to remain inline
with upstream expectations see:
https://github.com/altdesktop/playerctl#playerctld-autostart-issues

Checklist

• I have read CONTRIBUTING.md
• I have read Packaging.md
• I have built and tested my changes on my machine
• I will take responsibility for my template and keep it up to date

[q66]

you sure?

[ttyyls]

besides what i previously mentionned in the pr description, i tested it on my machine for a couple of days, and it indeed works.

However i still don't get why the service was supposed to be launched with dbus actvation as a result of a mpris client asking for metadata or a mpris command executed earlier yet neither trigger it for me...

As i understand dbus activation should result in a lingering process (analogous to notification daemons providing org.freedesktop.notifications) but in this case i don't see it, either way it'll be far from the first dbus activated service with a dinit service as well.

so maybe?