v8.5.5: add config for graceful shutdown

[hujiatao0]

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• This PR is translated from: v8.5.5: add config for graceful shutdown docs#22158
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[qiancai]

Suggested change

	### `graceful-shutdown-timeout`
	### `graceful-shutdown-timeout` <span class="version-mark">从 v8.5.5 版本开始引入</span>

[qiancai]

Suggested change

	+ graceful shutdown的超时时长，达到该时间后未完成转移的leader会跳过转移，节点直接进入停机流程。该值为0s时表示不启用graceful shutdown功能。
	+ TiKV 优雅关闭 (graceful shutdown) 的超时时长。
	+ 当该值大于 `0s` 时，如果关闭 TiKV 节点，TiKV 在该超时时间内会尽量将其上的 leader 副本转移到其他 TiKV 节点，然后再关闭。若达到该超时时间后仍有 leader 未完成转移，TiKV 将跳过剩余 leader 的转移，直接进入关闭流程。
	+ 当该值为 `0s` 时，表示不启用 TiKV 的 graceful shutdown 功能。

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