ddl_embedded_analyze.md: fix the format issue in title (#22037)

[ti-chi-bot]

This is an automated cherry-pick of #22037

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Summary of Changes

Hello @ti-chi-bot, I'm Gemini Code Assist[^1]! 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 introduces a new documentation page explaining the ANALYZE feature embedded within DDL statements in TiDB. This functionality, available from v8.5.4 and v9.0.0, automates the collection of statistics for newly created or reorganized indexes, such as those resulting from ADD INDEX or MODIFY COLUMN operations. The primary goal is to ensure that the query optimizer always has up-to-date statistics, thereby maintaining optimal query performance and preventing plan regressions that could occur if statistics were missing or outdated after schema modifications.

Highlights

• New Documentation Page: A new documentation page, ddl_embedded_analyze.md, has been added to describe the ANALYZE feature embedded in DDL statements.
• Embedded ANALYZE Feature: The document details how TiDB automatically runs an ANALYZE operation during DDL statements that create new indexes (ADD INDEX) or reorganize existing ones (MODIFY COLUMN, CHANGE COLUMN).
• Improved Optimizer Performance: This feature ensures that statistics for new or reorganized indexes are promptly updated, preventing inaccurate optimizer estimates and suboptimal query plans immediately after schema changes.
• Configurable Behavior: Users can control this behavior using the new system variable tidb_stats_update_during_ddl, which is OFF by default.

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