*: Add active-active doc

[lcwangchao]

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[ti-chi-bot]

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[lcwangchao]

/hold

[ti-chi-bot]

@lcwangchao: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	f0d6fdf	link	true	/test pull-verify

Full PR test history. Your PR dashboard.

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