Replace ronn for manpage generation

[mhashizume]

Facter uses the ronn gem for generating manpages. However, ronn and its dependencies (like hpricot) have been unmaintained for ~14 years.

Recently, Clang 16 has started raising errors for building native extensions for hpricot (as reported in Homebrew and also seen in FreeBSD). It seems unlikely that this will be fixed upstream, and we will probably see more issues with ronn and hpricot as time goes on.

Homebrew has recently gone through this process and ultimately ended up going with Kramdown: Homebrew/brew#16868

ronn-ng is also an option: https://github.com/apjanke/ronn-ng

pandoc is another option as it allows converting from markdown to roff. The pandoc-ruby gem provides ruby bindings for it.

[mhashizume]

We may also need to do this with Puppet.

[github-actions]

Migrated issue to FACT-3461