refactor(TwoFactorAuthentication): Remove references to old Duo SDK version 2 code and replace them with the Duo SDK version 4 supported library DuoUniversal code.
Increased unit test coverage in the Two Factor Authentication code space. We opted to use DI instead of Inheritance for the Duo and OrganizaitonDuo two factor tokens to increase testability, since creating a testing mock of the Duo.Client was non-trivial.
Reviewed-by: @JaredSnider-Bitwarden
