LG-15700 - Update mock proofer to handle passport YAML

[jmax-gsa]

🎫 Ticket

Link to the relevant ticket:
LG-15700

🛠 Summary of changes

Write a brief description of what you changed.

📜 Testing Plan

Provide a checklist of steps to confirm the changes.

• Running locally, create an account and enter verification.
• Select "upload images from this computer", and upload the file passport_credential.yml from the spec/fixtures directory.
• Verify that your passport credentials are accepted, and you're on the SSN page
• Cancel IdV and start over. Repeat the above procedure, but using the file passport_bad_mrz_credential.yml
• Verify that your passport credentials were not accepted. and you're on the 'try again' page.

[lmgeorge]

I only have one change for documentation but otherwise LGTM. (caveat I did a read-only review for the sake of time)