dm: add LOCK TABLES privilege note for managed MySQL sources (8.5)

[alastori]

Cherry-pick of #22605 to release-8.5.

Adds conditional LOCK TABLES privilege documentation for managed MySQL sources (RDS, Aurora) to dm-precheck, dm-worker-intro, and quick-start-with-dm.

See #22605 for full context.

Which TiDB version(s) do your changes apply to?

• v8.5 (LTS)

cc @GMHDBJD @qiancai

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[gemini-code-assist]

Summary of Changes

Hello, 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 enhances the documentation for TiDB Data Migration (DM) by providing crucial information regarding MySQL user privileges, specifically the LOCK TABLES privilege. It addresses scenarios where DM interacts with managed MySQL services like Amazon RDS or Aurora, where certain operations like FLUSH TABLES WITH READ LOCK might be restricted. The changes ensure users are aware of the necessary permissions for proper data consistency during migration.

Highlights

• Documentation Update for Managed MySQL Privileges: Clarified the requirement for LOCK TABLES privilege when using DM with managed MySQL services (like Amazon RDS or Aurora), especially when FLUSH TABLES WITH READ LOCK is restricted. This update affects dm-precheck, dm-worker-intro, and quick-start-with-dm documentation.

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[gemini-code-assist]

Code Review

This pull request adds documentation about the LOCK TABLES privilege requirement for managed MySQL sources like RDS and Aurora when using DM. The changes are applied to the precheck, worker introduction, and quick start guides. My review focuses on improving the clarity and style of the new documentation notes, suggesting minor rephrasing to use active voice and avoid abbreviations, in line with the repository's technical writing style guide.

[gemini-code-assist]

To improve readability and adhere to the active voice preference in the style guide, I suggest a minor wording change.

Suggested change

	- LOCK TABLES permission on the dump tables if `consistency=lock`, or if `consistency=auto` and the source is a managed MySQL service (such as Amazon RDS or Aurora) where `FLUSH TABLES WITH READ LOCK` is restricted
	- LOCK TABLES permission on the dump tables if `consistency=lock`, or if `consistency=auto` and the source is a managed MySQL service (such as Amazon RDS or Aurora) that restricts `FLUSH TABLES WITH READ LOCK`

References

1. The style guide recommends using active voice for clarity (lines 43-45). Changing 'where ... is restricted' to 'that restricts' improves readability. ^(link)

[gemini-code-assist]

To improve clarity and better align with the style guide, I suggest rephrasing this note. The proposed changes use active voice, address the user with 'you', and avoid an undefined abbreviation, making the note easier to understand.

Suggested change

	> **Note:** If migrating from a managed MySQL service (such as Amazon RDS or Aurora) where `FLUSH TABLES WITH READ LOCK` is restricted, the user also needs the `LOCK TABLES` privilege. DM's default `consistency=auto` mode falls back to `LOCK TABLES` for data consistency when FTWRL is unavailable.
	> **Note:** If you are migrating from a managed MySQL service (such as Amazon RDS or Aurora) that restricts `FLUSH TABLES WITH READ LOCK`, the database user also needs the `LOCK TABLES` privilege. This is because DM's default `consistency=auto` mode falls back to using `LOCK TABLES` for data consistency when `FLUSH TABLES WITH READ LOCK` is unavailable.

References

1. The style guide recommends writing in the second person ('you') (line 22), using active voice (lines 43-45), and ensuring clarity for the user (line 14). The suggested change addresses these points and also avoids an undefined abbreviation. ^(link)