Should be possible to set the tabstop size

**Is your feature request related to a problem? Please describe.**
It shows patches with a smaller tab space (4) than it should be (8).
There is a tabs(1) command: "The tabs program clears and sets tab-stops on the terminal."
But it has no effect on gitui.

**Describe the solution you'd like**
gitui should use either an environment variable or a config setting, or it should respect what the tabs(1) command sets.

**Additional context**
FreeBSD 14.0