doc: configs of max-ts checker

[ekexium]

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Doc of 3 TiKV config items, introduced in tikv/tikv#17917

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tikv/tikv#17916
tikv/tikv#17917

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[you06]

更新 max-ts 的时候这个路径应该永远不会 panic？

https://github.com/tikv/tikv/blob/615a6549cf6388367da874baa53937501c3efb88/components/concurrency_manager/src/lib.rs#L195

[ekexium]

补充了一句