Position the tab bar on top by default

Like it's done with _ShowCmdline, establish a single point to modify the default position of the tab bar, instead of the two existing places. Position the tab bar on top by default.

As it can be read on https://pointieststick.com/2022/12/02/this-week-in-kde-custom-tiling/ about Konsole and other apps:

"By default, Konsole’s tab bar is now located toward the top of the window like in most other apps, rather than at the bottom".

and on that merge request:

"Currently Konsole has its tabs on the bottom of the window. This is nonstandard; few to no other main views in KDE apps have their tabs on the bottom in the same manner."

Later, the user can change the tab bar position.