kcms/workspaceoptions: add paste-related keywords

Under Wayland, the (Workspace) General Behavior kcm allows enabling and disabling X11-style pasting of selected text. This is not fully advertised in the kcm JSON file; only middle click is listed there.

This change adds "copy,paste,selected,selection,primary" to the X-KDE-Keywords field for this kcm.

This is a somewhat extensive list, but the terms have no other hits when searching in System settings, or very few. Unfortunately, I don't think it's possible to have some terms only work on Wayland, so X11 users might see some unrelated suggestions on particular search terms, but "selected" and "selection" both also somewhat make sense there, as this kcm controls single-click selection vs activation.