SAML SSO authentication for merge request password approval

Problem to Solve

GitLab currently supports requiring user passwords to approve merge requests. However, this feature also requires the use of password authentication for the GitLab web interface. In many cases organizations are choosing SAML SSO/SCIM based solutions for their user account management on GitLab and so users don't have nor would organizations like for those users to have passwords to GitLab.

Proposal

When the setting for require user password to approve is enabled, if the option for password authentication is disabled, the button should prompt the user to re-authenticate with their currently configured and enabled sign-in provider(s).

Additional Details

There's a POC of some of this in !79876 (closed) - but it's also extending to support MFA authentication.