[Tech debt] Remove alembic autogenerate boilerplate

[TheAndrewJackson]

Description

Right now every new sqlalchemy model needs to be added to the base.py file for alembic's autogenerated migrations to work. It would be nice if this wasn't required. It's a small but easy step to forget when creating new models.

It might not be possible to eliminate the boilerplate. Further research is required to see if it can be done.