More tabline options

[d-miketa]

I quite like the tab line in this screenshot. It seems simple enough to emulate the tab look through tab_title_template and active_tab_title_template. Not sure about the left and right round "powerline" separators, but presumably you can set

tab_bar_style separator
tab_bar_separator ""

and place the separators manually into {active_,}tab_title_template.

Assuming that works, I'm only missing the option to centre the tab line. Would it be possible to add it in? Many thanks.