Add deprecate-integer-display-length to TIDB Config (#15379)

[ti-chi-bot]

This is an automated cherry-pick of #15379

What is changed, added or deleted? (Required)

Added docs for the undocumented deprecate-integer-display-length option.

See also: https://github.com/pingcap/tidb/blob/302786ffb91400f30d0be90abaca852a73ffa41c/config/config.toml.example#L102-L104

Note that I also filed a bug that is related to this issue: pingcap/tidb#46650

Also related: pingcap/tidb#18775

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

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• master (the latest development version)
• v7.4 (TiDB 7.4 versions)
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• v5.0 (TiDB 5.0 versions)

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

• This PR is translated from: Add deprecate-integer-display-length to TIDB Config docs#14718
• 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

[ran-huang]

/approve

[ti-chi-bot]

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