test(django-cf): add more tests using django ORM

[ryanking13]

More test improvements using django ORM.

• Adds tests using django orms, such as model.objects.create(). Previously what we mostly was using a raw query (run_query("INSERT ...")), which was less django-style
• Add test coverage for DO backend + ORMs
• Add test coverage for using Django's FileField API, which uses R2 backend internally.

[ask-bonk]

LGTM

github run