Something like tab_bar_begin_template and tab_bar_end_template?

[ryanerwin]

Is your feature request related to a problem? Please describe.
I'm trying to emulate my tmuxline.vim style status bar in Kitty

Describe the solution you'd like
I would like to have options similar to tab_title_template that apply to the beginning and end of the status line.

For example, at the beginning of the line I would like to have the kitty window number, and at the end of the line, I would like to have the system name. Anything that you would put in a vim statusline or i3bar might be a good candidate for the status bar.

Describe alternatives you've considered
This is just a nice to have.... Would be nice include more information into the status bar.
Of course we can use kitty productively without that - just a nice to have.

Additional context
The current tab_title_template works great! Currently I'm using:

tab_title_template "{index}  {title[:5]}"

On top is my tmux statusline. On the bottom is my Kitty tab bar

[kovidgoyal]

This isnt something that's worth the effort to me, but a PR is welcome.
Note that as far as status lines are concerned, my plan is to implement
something along the lines of: #2391 for a general solution