cloud: add SQL and TiFlash related docs (#9001) (#9479)

[ti-chi-bot]

This is an automated cherry-pick of #9479

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[ti-chi-bot]

@ti-chi-bot: PR needs rebase.

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❌ qiancai

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[qiancai]

/close

[ti-chi-bot]

@qiancai: Closed this PR.

In response to this:

/close

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