HDDS-10205. Upgrade Docusaurus to 3.1.0

[errose28]

Summary

Docusaurus 3.1.0 was released earlier this month: https://docusaurus.io/blog/releases/3.1
It includes some bug fixes and a new feature to fail the build on broken markdown anchor (header) links.

Jira

HDDS-10205

Testing

Site remains functional in the following deployments:

• Dev server: pnpm run start
• Prod build: pnpm run build && pnpm run serve
• Docker image: docker compose up --build # --build to build a new image with the updated dependencies

TODO

• There is a build time regression for 3.1.0 reported recently and fixed in perf(core): optimize broken links checker facebook/docusaurus#9778. It does not affect this site (build time is still 5 seconds with the changes) but let's wait a bit to see if a patch release is published.

[errose28]

Switching to a new branch and closing this PR.