feat!: use XDG conventions on macOS too

[utkarshgupta137]

~/Library/Application Support is an utterly inconvenient location for macOS users. Most CLI tools follow the XDG conventions on macOS as well. Replace the dirs crate with the etcetera crate to support it on macOS as well. Config locations for other platforms are unaffected.

Closes #534.
Closes #539.
Closes #540.
Closes #541.

[fujiapple852]

Thank you for the PR @utkarshgupta137!

I'm a macOS user and agree that ~/Library/Application Support is not somewhere I'd typically place config files for command line tools. I'd say we can drop the macOS specific dir entirely and use only XDG for nix.

Given an alternative to the dirs crate is needed anyway due to the new licensing, and given we need something more than the home crate, I think etcetera may be a suitable alternative.

I've reworked the code slight, I've pushed a fixup commit in #539 with my suggested changes, if you're happy with them then please cherry pick to your PR and squash the commits. I've added comment to this PR explaining the changes I've made in my PR.

Thanks!

[utkarshgupta137]

@fujiapple852 I've included your changes & made a small modification to call choose_base_strategy only once. It calls home::home_dir, so it is better to not call it twice.
Also, feel free to update this PR if you want.

[fujiapple852]

LGTM

[utkarshgupta137]

Good to merge