Update minimum value for initial-scan-rate-limit

[RidRisR]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

Update minimum value for initial-scan-rate-limit.

Which TiDB version(s) do your changes apply to? (Required)

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• master (the latest development version)
• v8.0 (TiDB 8.0 versions)
• v7.6 (TiDB 7.6 versions)
• v7.5 (TiDB 7.5 versions)
• v7.4 (TiDB 7.4 versions)
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• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

What is the related PR or file link(s)?

tikv/tikv#16485

• This PR is translated from:Update minimum value for initial-scan-rate-limit docs#16549
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[CLAassistant]

All committers have signed the CLA.

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-12 00:18:23.303572663 +0000 UTC m=+731130.325819044: ☑️ agreed by hfxsd.
• 2024-03-14 03:39:04.913655459 +0000 UTC m=+915971.935901847: ☑️ agreed by Oreoxmt.

[hfxsd]

/approve

[ti-chi-bot]

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