Incubation of Plasma-Login-Manager

[David Edmundson]

Plasma login manager is based off of SDDM, but with reduced
requirements with the intention of then being able to deliver tighter
integration with Plasma's requirements

https://invent.kde.org/plasma/plasma-login-manager

Some discussions can be found at
https://invent.kde.org/plasma/plasma-desktop/-/issues/91. It's also
been discussed on plasma-devel since, this is following up on the
official process.

The incubation checklist is available on
https://invent.kde.org/plasma/plasma-login-manager/-/issues/2

Some things don't really apply as it's not a traditional app.

David