Add "Always On Top" as a pushpin icon next to the minimise, maximise and close icon in the program bar [Feature Request]

[mofosyne]

I find that I would like to keep windows on top, especially terminal or widget style programs. Or text notes.
You already got "Always On Top" but it's a hidden in submenus.

I think it's worth exposing as a quick button with an icon that looks like a push pin. If you press it the icon should look like a pinned icon.

[Secret-chest]

Having it always visible would be overkill. And I don't think GTK+ supports more buttons.