Register all models with Django Admin

[brylie]

We haven't registered all project models with the Django Admin, making it difficult to manage content in a centralized manner.

Task

For each model in our project,

• [ ] register the model with the Django Admin, if not already registered

Resources

• https://docs.djangoproject.com/en/4.1/ref/contrib/admin/#modeladmin-objects

[kishan3]

Fixed in #130