ENG-8410 Rename UserAttribute to PeopleAttribute

[[id:1616c676-e2f4-4982-917f-a3e46f4a0fce][Renaming Django Models]]

- A fun exercise in renaming a Django model today. Thankfully there's not much

data in any of these tables. The biggest issue right now is making sure I've

found all the references and that the migration works.

- I'm not totally sure I'm going about this all the right way. At some point the

black PR will be merged and I'm going to have to clean up these two branches

either by rebasing or just cherry-picking the commit to a new branch. We'll

see what's easier soon.