fix: include link for release notes

[sunng87]

What changed

Include toc links

Scope

• Documentation versions:
• Languages:

Verification

Checklist

• I verified the content against the applicable GreptimeDB version.
• I updated the relevant documentation versions and languages, or explained why not.
• I checked changed links and anchors.
• I updated navigation when the document structure changed.

[sunng87]

backport! 1.2

[github-actions]

✅ Backport completed successfully for version 1.2

Changes have been committed to this PR branch.

[cloudflare-workers-and-pages]

Deploying greptime-docs with    Cloudflare Pages

Latest commit:	4199674
Status:	✅  Deploy successful!
Preview URL:	https://afc817f8.greptime-docs.pages.dev
Branch Preview URL:	https://docs-ee-release-notes-toc.greptime-docs.pages.dev

View logs

[killme2008]

LGTM

[sunng87]

Addressed the review feedback in 4199674 (applied to both nightly and 1.2, en + zh):

1. v1.2 engine base link — the intro now links to /release-notes/release-1-2-0.
2. Query spill — reworded: no longer framed as an enterprise capability; noted it has been open-sourced in the GreptimeDB engine (v1.3.0-alpha.1, greptimedb#8884) with a link to those release notes.
3. Iceberg table engines — the bullet now spells out the full engine coverage: default mito engine tables plus metric-engine physical tables are exported; logical metric tables are not exposed (query the physical table directly).