Add value range for the search backpressure settings

[gaobinlong]

Description

In 2.18.0, we add more strict validation for the search backpressure settings, we need to document the new change and the existing value range for those setting.

Issues Resolved

No issue.

Version

2.18.0

Frontend features

No change

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.
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[github-actions]

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[kolchfa-aws]

Thank you, @gaobinlong! Made some suggestions to reduce the cognitive overhead on the user.

[natebower]

@gaobinlong @kolchfa-aws LGTM!

[kolchfa-aws]

@gaobinlong Let me know when the code PR is merged, and we can merge this one.

[gaobinlong]

@gaobinlong Let me know when the code PR is merged, and we can merge this one.

Thanks @kolchfa-aws, the code PR has been merged yet.