docs: document scanbench query suites and results

[evenyag]

What changed

Document scanbench query suites and structured results introduced in GreptimeTeam/greptimedb#9050. Add a named suite example and explain ordered execution, configuration validation, iteration restrictions, generated names, and warmup statistics.

Describe --result-file, result format version 1, normalized projections, timing/size units, partition statistics, and write-on-success behavior. Update the option reference and verbose-output description while preserving existing single-request examples and headings.

Closes #2828

Scope

• Documentation versions: Nightly
• Languages: English, Chinese

The upstream feature is 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
• Verified suite validation, run ordering, warmup behavior, result serialization, and failure handling against upstream source and its serialization test fixture.
• Parsed JSON examples and checked supported config fields, mutually exclusive projections, and suite names.
• Checked matching English/Chinese code examples and preservation of existing headings.
• No benchmark was run against a deployment.

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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