Make the files view filtering setting persistently configurable

Is your feature request related to a problem? Please describe.

I almost always prefer to show only tracked files in the files view. However, this cannot be configured persistently in Config.yml, only at runtime.

Describe the solution you'd like

Add a setting to Config.yml so that lazygit can start up with my preferred filter.

Describe alternatives you've considered

The only alternative is just pressing C-b t every time I start up lazygit, as far as I can tell.

Additional context

The functionality was added in #4226 and #4230.

I have not submitted this as a PR as per the contributing instructions. However, I do have this implemented and working (including hot-reloading, but I need a bit of advice on the codebase to make that cleaner).