Provide guidance on updating email

What does this MR do and why?

Provide guidance on updating email

part of: https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/442

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the feature flag in Rails console

   Feature.enable(:require_email_verification)

2. Sign out
3. Sign in 3 times with a wrong password
4. Sign in with your correct password
5. Click Update email

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.