Autogenerate API docs

Our format for API docs is great, but as they are manually created I can see how they can get out of sync quickly when we are making changes. We shouldn't do this before launch, but I wonder how we can autogenerate API docs, kind of like how we do wirth `make gen` on coder/coder

Start by reviewing how the current API docs are manually created and compare that process with `make gen` in coder/coder. Define what API sources and generated output would be involved; the work is done when the documentation can be regenerated reliably and stays aligned with API changes.

索引モデルが issue の本文から書いたものです。