sysutils/consolekit2: Make ck-system-* scripts user editable

This might be needed when using alternatives to init(8), like
sysutils/runit-faster, which do not react well to signals send by
shutdown(8)/reboot(8) and where you have to use other commands,
like runit-init {0,6}. By updating the ck-system-* scripts to run
them instead, we can actually make use of things like the Xfce4
logout dialog or Kodi's shutdown dialog with runit-faster. But to
make this permanent across updates the scripts have to be installed
as sample files.

PR: 236445
Submitted by: tobik
Approved by: gnome (maintainer timeout, 14 days)