closes: https://github.com/TryGhost/Ghost/issues/14981
- Taxonomy-specific sitemaps were invalid xml when there was no data
- These invalid empty sitemaps were referenced in the index sitemap causing SEO tools to report errors
refs https://github.com/TryGhost/Toolbox/issues/354
- this commit turns the Ghost repo into a monorepo so we can bring our
internal packages back in, which makes life easier when working on
Ghost