cdc: make mq encoding protocol related more clear (#19156)

[ti-chi-bot]

This is an automated cherry-pick of #19156

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• This PR is translated from:cdc: make mq encoding protocol related more clear docs-cn#18783
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[ti-chi-bot]

@ti-chi-bot: 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	a589f93	link	true	/test pull-verify

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