AAI-223 Add a 'registration_from' field to app_metadata so we can show app-specific email verification

[marius-mather]

Description

AAI-223: We need a way to let Auth0 know which app the user signed up from, so we can show app-specific info on email verification pages. Adding a field to app_metadata seems like a good way to do this

Changes

• Add registration_from to app_metadata schema
• Add it when creating registration data for each app
• Tests

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

How to Test Manually (if necessary)

Run uv run pytest