Add a new standalone executable to replace X-KDE-Autostart-Condition

Summary:
For systemd autostart generator will add a ExecCondition=kde-systemd-start-condition rcfile:section:entry:default
As described in T12627. Needs D28421

Test Plan:
Run kde-systemd-start-condition; should return 0 with a missing or incomplete argument, 255 with a false or non-existent and non-default con
fig value.

Reviewers: davidedmundson, broulik, dfaure, ngraham, meven

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28424