docs: Add 503 response code to core-command API document

[jinlinGuan]

Fix #3838

Signed-off-by: Ginny Guan [email protected]

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Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?) N/A, only update API doucment
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• I have opened a PR for the related docs change (if not, why?) N/A, only update API doucment

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[sonarqubecloud]

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1.1% Duplication

[cloudxxx8]

LGTM