KDE Plasma 6.8 for LinuxDoors -- headless, over VNC.

Plasma 6.8 is Wayland-only (it has no X11 session any more), so it can't be
shown through x2go's normal X11 display. LinuxDoors keeps Plasma 6.7.5 (X11)
as its regular KDE desktop and installs Plasma 6.8 beside it in /opt/plasma68.

To use it, connect with "X2Go Client Wayland" (package x2goclient-wayland)
and pick the session type "Plasma 6.8 (VNC)". On the server that runs
/opt/plasma68/bin/linuxdoors-plasma68-vnc, which starts Plasma 6.8 on a
virtual screen and serves it with krfb on 127.0.0.1:5901 (reached only
through x2go's SSH tunnel). Plasma 6.8 keeps its own settings in
~/.config/plasma68, ~/.local/share/plasma68 and ~/.cache/plasma68, so your
Plasma 6.7.5 desktop settings are never touched.
