feat: adds option to hide clean flag

[joshmedeski]

Purpose

Adds the option for a user to hide the clean flag. I, personally, would rather not see anything as an indicator that everything is clean.

Approach

Add a hide_clean option that defaults to false and when set to true will not render the clean flag.

[arl]

Thanks @joshmedeski Can you add some test please? No need to be fancy, just a single test case showing off the feature. Many examples are https://github.com/arl/gitmux/blob/main/tmux/formater_test.go

[joshmedeski]

All done, thanks :)