[server] Document API Endpoints

[rhinodavid]

Some of the API endpoints (packages/upswyng-server/src/routes/api/**) have comments explaining what the endpoint does, what the request should look like, and what a successful and error response look like, but some don't.

We should select a standard way of documenting these (maybe APIDoc?) and complete documentation. We could also add a script to generate an API manual from the docs.

[amites]

How's openAPI sound?

you start with yaml or json (yaml often easier to edit by humans)
https://swagger.io/specification/

and get outputs like
https://petstore.swagger.io/v2/swagger.yaml

[amites]

Started on a yaml openapi doc -- documents the GET categories endpoint so far

likely to put on hold until I hear input that this is a good direction

https://github.com/CodeForBoulder/upswyng/pull/481/files

[amites]

PR ready to review -- let me know if there should be more than the /api endpoints

ie: /provider

to login and others