Add JH check for restricted country

What does this MR do and why?

Related issue: #450796
Related JiHu issue: https://jihulab.com/gitlab-cn/gitlab/-/issues/4412

We previously introduced a new feature: based on geographic information, prohibit users from China from registering. But this logic should NOT be executed in the JiHu environment because all JiHu users are from China. 😄

The current MR adds a JiHh judgment for this restriction.

MR acceptance checklist

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Screenshots or screen recordings

No UI changes.

How to set up and validate locally

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