Improve types and docs around FastAPI Http Endpoints

[jeffchuber]

Some users want to directly use the Http endpoints from the FastAPI server. We should improve the naming, types, docstrings, and docs around this.

@HammadB @atroyn how would we feel about make this more of a "external service"? I know in the past we have thought of it as more "internal"

http://localhost:8000/docs exists, but we can do better.