Allow the gitlab-jh codebase to override recaptcha module to avoid getting blocked in China

What does this MR do?

Google recaptcha's domain(www.google.com/recaptcha) is blocked in China. To solve this problem in JH edition. To solve it, we just need to allow the gitlab-jh codebase to override the Recaptcha module in /lib/gitlab/recaptcha.rb, call the prepend_mod at the end of this file will make /jh/lib/jh/gitlab/recaptcha.rb active(see this MR). This will only affect the gitlab-jh edition's feature.

Conformity

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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team