Add an option to disable middle-click pasting

[tukusejssirs]

I use TrackPoint and middle button also serves as a way to scroll by pressing it and moving the TrackPoint.

Now, I personally don’t use primary clipboard, thus I wish to disable it, but in Sway (my prefered window manager) disabling it does not work as expected (even though it should) and the apps/programs are still able to utilise it.

---

Related: swaywm/sway#4511