Adds account management 2FA workflow

Why is this change being made?

User accounts in account management projects are generally free users and don't qualify for independent account ownership verification. However, it's in GitLab's interest to process these requests so we can collaborate with our customers.

Since such accounts, generally, don't have enough information to properly verify an identity we should consider using a modified "large customer" workflow where the customer themselves independently performs identity verification and authorizes GitLab to make the change.

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