Advanced Sitemap with the right lastmod values

[julien-deramond]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

97b27ba removed the Sitemap semi-advanced generation because the content was not correct since the modification date was global to the website.

It doesn't seem possible right now but the idea of this feature request would be to use the data stored in the frontmatter for articles, chapters, modules, etc. to have the right lastmod value in the sitemap.

serialize function in @astrojs/sitemap seems to be the best shot right now but doesn't seem to allow to get info from the frontmatter.

Motivation and context

changefreq and priority are ignored by Google but it is probably not the case for lastmod even if I'm not certain about it. Hopefully it would help with the SEO of the website.