Add phone verification code enabled

What does this MR do and why?

Add phone_verification_code_enabled to control whether Real name system enabled or not. Default value is false, when we deploy to production environment, we should update it to true to enable Real name system.

Related to upstream MR https://gitlab.com/gitlab-org/gitlab/-/merge_requests/86844

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.