Consider `dirs` crate for better cross-platform support

[maxrake]

Consider better cross-platform support by creating/saving/updating the settings.yaml file in a more natural location for the OS. This can be accomplished with the dirs crate from crates.io. Currently, a local crate with the same name is used - cli/src/dirs.rs - and assumes Linux for the default location.

References:

• https://github.com/phylum-dev/phylum-ci/pull/474#discussion_r1784370249
• Documentation for dirs crate

[kylewillmon]

The dirs crate was considered when moved files out of ~/.phylum.

The crate uses locations that are technically correct for each OS, but that means using the very unnatural $HOME/Library/Application Support on macOS...

Since the only concern with our current code is Windows, it probably makes more sense to update our code to use AppData on Windows rather than switching to the dirs crate for everything.

[maxrake]

Reminder for possible later phylum-ci update: there is a Python package, platformdirs, that does the same thing as the dirs crate.