[Feature Request]: Text alignment in buffer tabs

### What?

Would like the option to choose text alignment in buffer tabs (i.e. mode="buffers"). Could not find any options for doing this in the config. There is an option for aligning the text in the offset area, so I imagine it will be something similar to that: A simple buffer_text_alignment option in the config allowing 'center' | 'left' | 'right'. This might of course be more complicated than it seems at a first glance due to all the other possible options (e.g. separator style might be slanted, close button might or might not be present), so I imagine it would be easiest to have it for the 'thin' setting as a start?

### Why?

Just seems like a thing that should be adjustable. Also, it is my personal preference having buffer names left aligned and the centering just does not look that good to me.