Add identity_verification_auto_ban feature flag to disable auto banning

What does this MR do and why?

Add a by default enabled identity_verification_auto_ban feature flag to disable auto banning when users try to verify their identity with a previously banned phone number or credit card.

Issue: https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/317

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.