Allow custom registry to get the actual address for registering

[XiaoYi-byte]

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docs: Documentation only changes

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自定义的 Registry 获取 Client 可访问的实际地址，增加这部分的文档

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Name	Status	Preview	Comments	Updated (UTC)
cloudwego	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 30, 2024 5:30am

[felix021]

LGTM, will merge it after https://github.com/cloudwego/kitex/pull/1333 is ready