feat: add <lastmod> to sitemap

[pmarschik]

Pre-flight checklist

• [x] I have read the Contributing Guidelines on pull requests.
• [x] If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• [ ] If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Add <lastmod> to sitemap, should fix https://github.com/facebook/docusaurus/issues/2604.

Test Plan

Extend existing sitemap tests to expect generated lastmod date.

Test links

Deploy preview: https://deploy-preview-_____--docusaurus-2.netlify.app/sitemap.xml

Related issues/PRs

• https://github.com/facebook/docusaurus/issues/2604

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[github-actions[bot]]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 59	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/installation	🟠 89	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/category/getting-started	🟠 77	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog	🟠 75	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 64	🟢 97	🟢 100	🟢 100	🟠 89	Report
/blog/tags/release	🟠 76	🟢 100	🟢 100	🟠 80	🟠 89	Report
/blog/tags	🟠 77	🟢 100	🟢 100	🟢 90	🟠 89	Report

[ardeche07]

Thanks for submitting this @pmarschik ! Have you gotten any feedback on this PR? We use Docusaurus at Unleash and were just trying to add last mod to our docs since it is becoming increasingly important for Google. Would love to see this merged.

[pmarschik]

@ardeche07 I've not gotten any feedback, however I've been using the changes for our published docusaurus page for some time. When I get around it, I'll update the PR with the latest changes (its not actually 170 files changed, this PR was based on docusaurus v2)

[pmarschik]

Thanks for your contribution @pmarschik and sorry for the late review

Thank you for reviewing the MR @slorber.

Your PR is not really in a state I could merge, and try to implement things that are not really needed according to Google recommendations.

It should also target main and not docusaurus-v3 branch

I'm aware, this is just what I use to pnpm patch our build and have a working lastmod until the feature is available upstream.

Let me know if you want to give it another try, otherwise I'll create another PR.

I'm currently occupied with other projects and I don't know when I next have time to circle back to this. So I think it would be best if you create another PR.

[slorber]

Thanks

I'll close this one in favor of a new one, track https://github.com/facebook/docusaurus/pull/9954