docs: publish Paimon and PyPaimon 2.1.0

[XiaoHongbo-Hope]

Summary

• Publish the 2.1.0 release note scoped to the approved tag.
• Update both signed source downloads, PyPI/Maven examples, the version menu and docs deployment versions.
• Include the Scala binary suffix in Spark artifact names.

Validation

• Full pnpm build, Markdown parsing, 25 prerendered routes and header ESLint passed.
• Browser-checked the release page, download links and documentation menu.

Deployment order

Merge the release-2.1 documentation configuration first: apache/paimon#10517.
Master navigation: apache/paimon#10518.
Rust release documentation: apache/paimon-rust#1114.
Then deploy the website and verify /docs/2.1 and the public release/download pages before announcing.

No release tag or published package changes.

[JingsongLi]

+1