Add all migrations that are missing from model changes

[ericholscher]

Fixes #4201

[stsewd]

What about adding the check for missing migrations on this PR too?

./manage.py makemigrations --check --dry-run

[ericholscher]

I'm still not convinced having a CI check for migrations is a good idea. It just feels like we're going to accumulate a ton of migrations, and have issues with them conflicting :(

But I'm 👍 on getting it in there and seeing how it plays out.