Add complex return types (pydantic models) to the docs pages

Many of the API endpoints return a pydantic model, or a collection of them. However, each endpoint docs page only mentions them by name. It could be useful to output the model definitions somewhere in the docs, so that users don't have to navigate into the code to find them.

Ideally this docs info can be auto-generated in the same way as the current pages. Mostly the models correspond to the Central API response objects, so a direct link (if stable) could help as well.

Start by examining how the current API endpoint documentation pages are generated and how their pydantic return models are identified. Determine whether model definitions can be included directly or linked to stable Central API response objects; done means the generated pages expose complex return types without requiring users to inspect the code.

Written by the indexing model from the issue text.