v8.5.4: Add docs for Analyze Embedded in DDL and new system variable (#22014)

[ti-chi-bot]

This is an automated cherry-pick of #22014

Introduces the 'Analyze Embedded in DDL' feature documentation and adds a new page describing its behavior for index creation and reorganization. Updates TOC to include the new doc and documents the 'tidb_stats_update_during_ddl' system variable, which controls this feature.

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• This PR is translated from:Add docs for Analyze Embedded in DDL and new system variable docs-cn#21031
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[gemini-code-assist]

Summary of Changes

Hello @ti-chi-bot, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates documentation for TiDB's new 'ANALYZE Embedded in DDL' feature, which automatically collects statistics for newly created or reorganized indexes during DDL operations. This enhancement aims to prevent performance degradation from outdated or missing statistics, ensuring the optimizer always has current information. The PR also documents the tidb_stats_update_during_ddl system variable, allowing users to control this behavior.

Highlights

• New Feature Documentation: Added comprehensive documentation for the 'ANALYZE Embedded in DDL' feature, explaining its purpose and behavior during index creation and reorganization.
• System Variable Documentation: Introduced documentation for the new tidb_stats_update_during_ddl system variable, which controls the 'ANALYZE Embedded in DDL' feature.
• Table of Contents Updates: Updated the Table of Contents in both TOC.md and TOC-tidb-cloud.md to include the new documentation page.

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[gemini-code-assist]

Code Review

This pull request introduces documentation for the 'Analyze Embedded in DDL' feature and the corresponding tidb_stats_update_during_ddl system variable. The changes include a new documentation page and updates to the table of contents and system variables documentation. My review focuses on improving clarity, consistency, and adherence to the documentation style guide. I've provided suggestions to correct heading case, grammar, and ensure consistent use of backticks for code elements.

[hfxsd]

/approve

[ti-chi-bot]

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