docs: document missing SST manifest fields

[evenyag]

What changed

Document max_row_group_uncompressed_size (bytes, with zero meaning unknown) and nullable partition_expr in SSTS_MANIFEST, following GreptimeTeam/greptimedb#8965. Add a query for inspecting the new fields and update the illustrative output.

Also restore the previously omitted index_version and num_series fields so the complete displayed schema matches upstream column order, types, and nullability.

Closes #2795

Scope

• Documentation versions: Nightly
• Languages: English, Chinese

The new fields are not included in the existing 1.2 or older documentation releases.

Verification

• DOC_LANG=en pnpm check:links (includes the English production build)
• DOC_LANG=zh pnpm check:links (includes the Chinese production build)
• git diff --check
• Compared all 26 documented columns with the upstream ManifestSstEntry::schema definition.
• Reviewed field semantics against manifest-to-record-batch conversion and Mito manifest inspection.
• Checked English/Chinese example and schema consistency.

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.
• Navigation does not require an update because this extends an existing page.

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[killme2008]

@evenyag Merged. If a backport is needed, please open a separate PR.