Fix os.family references for Arch and Gentoo-based distributions

[zbentley]

Pull Request (PR) description

Switches to matching Gentoo and Arch via os.family instead of os.name.

Previously, code handled Manjaro/Gentoo/Arch-vanilla by checking if the name was "Gentoo", or if it started with "Arch" or "Manjaro" and ended with nothing or "linux". Facter already uses equivalent logic to generate the os.family fact, here, so it doesn't need to be reimplemented in this module: https://github.com/puppetlabs/facter/blob/main/lib/facter/util/facts/facts_utils.rb#L24

Side effects:

• All Arch distributions, vanilla and non (including Manjaro, Artix, CachyOS, and so on) should now be supported.
• Gentoo distributions with a custom OS name (more common than you'd think) would now be supported.

This Pull Request (PR) fixes the following issues

Fixes #332