[Feature Request] Split OpenAPI schema into multiple files

[shu8]

Is your feature request related to a problem? Please describe.
Our OpenAPI schema is now over 5k lines long which makes it very difficult to do anything with really, especially reviews.

Describe the solution you'd like
In #3389, @hueyy suggested splitting it out into multiple files per section (e.g., workspaces, resources, timetable, etc.).

Describe alternatives you've considered (optional)
Alternatively, we could try to integrate this into our use of Django itself: https://www.django-rest-framework.org/api-guide/schemas/ looks useful.