Feature(Config): Check XDG Config Directory on Mac

[ocboogie]

Most people on Mac wouldn't actually use the ~/Library/Application Support directory but rather ~/.config (see xdg-rs/dirs#45). This allows people to use their dotfiles on Linux and Mac. We could either make a breaking change and not use ~/Library/Application Support or we could check both directories for the config file. However, if we go the route of #283, there would have to be a decision to make: create the default config in ~/Library/Application Support or ~/.config.

Related:
xdg-rs/dirs#45
#283

[qballer]

I'm for r ~/.config

[a-kenji]

@ocboogie

This check should be now on main, can you please confirm that it works?
It checks after /Users/Alice/Library/Application Support/org.Zellij-Contributors.zellij,
so if you have that directory it will still load from there.

[a-kenji]

This should be adressed.