Use GitLab UI styled checkbox on help page form

What does this MR do and why?

Migrates admin help settings checkbox. Example commit of previous port 9df3f64a

Closes #358286 (closed)

Screenshots or screen recordings

before	after

How to set up and validate locally

Admin > Settings > Preferences > Sign-in and Help page

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.