Make automatic terminal title optional

**Is your feature request related to a problem? Please describe.**
Terminal title is force-set and not cleared on exit.

**Describe the solution you'd like**
Just make it optional.

**Describe alternatives you've considered**
None, there is only one true way in this case - make it optional :-)

**Additional context**
~~Happy to work on this feature.~~ https://github.com/gitui-org/gitui/pull/2832

Ref. https://github.com/gitui-org/gitui/issues/2484#issuecomment-3696312684