feat: Support hreflang tags for i18n

[jclusso]

Summary

What are your thoughts on adding support for hreflang tags so sites are generated with proper linking between pages. https://developers.google.com/search/docs/specialty/international/localized-versions#html

We currently have this helper in our sites

class Helpers::HreflangHelper < SiteBuilder

  def build
    helper :hreflang_tags_for do |resource|
      site.tmp_cache["href_lang_#{resource.path}"] ||=
        resource.all_locales.sum('') do |local_resource|
          tag.link(
            rel: 'alternate',
            href: "#{site.config.host}#{local_resource.relative_url}",
            hreflang: local_resource.data.locale
          )
        end.html_safe # rubocop:disable Rails/OutputSafety
    end
  end

end

[jaredcwhite]

Yeah, I love that idea! I'm about to dive back into the i18n stuff a bit to try to add Fast Refresh support, so I'll come back with a fresh perspective on how we could add this.