sddm: Add screen locker

Project:Linux software
Component:Documentation
Category:feature request
Priority:normal
Assigned:Unassigned
Status:active
Related pages:#9199: Simple Desktop Display Manager (SDDM) :-:-: #11001: KDE Plasma 5 and KDE 5 applications Regressions
Tags:Regression, sddm, Session locking
Description

see:
https://github.com/sddm/sddm/issues/773