Start adding REST API endpoint docs

[abkfenris]

An initial pass at including the API Endpoints in the docs. FastAPI isn't including the return types when available in the OpenAPI spec, which I haven't spent too much time debugging.

This depends on running docs/source/api/generate_openapi.py before generating the docs and after any changes that may change the endpoint signatures. It's not required to be run to work on other parts of the docs, those sections should error and be blank instead.

Additionally did a little re-arranging of the API docs, and added sections for each included plugin.

Rendered PR docs:

• All endpoints
• Plugins and their endpoints

Works on #55

[abkfenris]

And apparently I have an old version of FastAPI locally.

[abkfenris]

I think that changed in 0.78.0 https://github.com/tiangolo/fastapi/releases/tag/0.78.0 so clearly,

python -m pip list | grep fastapi                                         
fastapi                       0.77.1