migrate away from deprecated jsonfield package

### Describe the issue

The jsonfield package has been deprecated as of version 3.2.0. Migrate to Django's internal JSONField instead.

https://pypi.org/project/jsonfield/3.2.0/

### Code of Conduct

- [x] I agree to follow the [IETF's Code of Conduct](https://github.com/ietf-tools/.github/blob/main/CODE_OF_CONDUCT.md)