docs: clarify max-ts max-drift constraint

[ekexium]

What is changed, added or deleted? (Required)

Clarify that storage.max-ts.max-drift must be greater than cache-sync-interval, otherwise TiKV rejects the configuration.

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

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)

What is the related PR or file link(s)?

• Other reference link(s): tikv: add max-ts configuration docs for v8.5.7 #21745 (comment)

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

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[Copilot]

Pull request overview

Clarifies the TiKV storage.max-ts.max-drift configuration constraint to prevent invalid configurations (where max-drift is not greater than cache-sync-interval) from being used.

Changes:

• Document that storage.max-ts.max-drift must be greater than storage.max-ts.cache-sync-interval, otherwise TiKV rejects loading the configuration.
• Keep the existing recommendation to set max-drift to at least 3× cache-sync-interval.

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