Add email confirmation as mandatory step for unverified mentor emails

[dzmitry-varabei]

Please add a mandatory email verification step for mentors who have not previously verified their email during the registration process.

Steps to Reproduce:

1. Mentor navigates to the mentor registration page: https://app.rs.school/registry/mentor.
2. Mentor fills out the registration form and provides their email address (required field, may have been provided previously).

If the email is not verified, before proceeding to the "Done" step, an email confirmation screen should be displayed.

Expected Behavior: An email verification step is included in the registration process, preventing mentors from completing registration without verifying their email.