LG-10660: Consolidate MFA setup controllers

[aduth]

🎫 Ticket

LG-10660

🛠 Summary of changes

Updates links and updates capability of TwoFactorAuthenticationSetupController to handle both initial and additional MFA setups, with planned follow-on pull request to remove MfaSelectionController.

📜 Testing Plan

1. Go to http://localhost:3000
2. Create an account, up to "Authentication method setup"
3. Observe no visual differences from main
4. Set up an MFA method
5. When prompted, choose to "Add another method"
6. On the additional MFA setup screen, observe no visual differences from main

Also try a few variations:

• Choosing "Face or touch unlock" as your first MFA should hide the option to skip when setting up second method (LG-10235: Hide skip MFA after adding F/T #8739)
• MFAs added and single-only restrictions should apply (Kmas lg 9961 more mfa same type #8863)

👀 Screenshots

There should be no visual differences, aside from the URL in the additional MFA setup:

Before: /second_mfa_setup
After: /authentication_methods_setup

Screen	Before	After
Initial
Second

[kevinsmaster5]

Code looks good to me. Can confirm that it works as described.