MFA Frontend Improvements

What does this MR do and why?

Improves MFA front end:

• Revert min length of username from 4 > 3
• Adds error when users are not entering a username
• Adds border around QR code which makes scanning much easier
• Resolves #561 (closed)

Screenshots or screen recordings

How to set up and validate locally

• Add new MFA and scan QR code
• Verify MFA without inputting name

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• Have you checked this doesn't interfere/conflict/duplicate someone elses work?
• Have you fully tested your changes?
• Have you resolved any lint issues?
• Have you assigned a reviewer?
• Have you applied correct labels?