Draft: Add ability to disable private profiles - frontend changes

What does this MR do and why?

Adds frontend changes for gitlab-org/gitlab#421310 (closed). Please refer gitlab-org/gitlab!135431 (merged) for backend changes

Screenshots or screen recordings

How to set up and validate locally

1. Run migrations
2. Enable feature flag disallow_private_profiles

   Feature.enable(:disallow_private_profiles)

3. Make sure you have valid license to access premium features
4. Visit Admin Area > General > Account and limit
5. A new checkbox field with name Make new users' profiles private by default is available

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.