Support "examples" documentation

[tyree731]

As far as I can tell, nothing in this module allows you to specify example responses for different models. It would be nice if, perhaps through some decorator applied to a method on a pydantic model, one could provide an example response that the API might return, having that example response propagated through to the openapi spec and documentation.

[nkwade]

I second this, I was searching for how to provide an example response. I have to put an example response in my docstring now which will just look weird and people would have to look thru 2 "example response" section. Just being able to edit this myself would be great.

[pgjones]

This is already possible with Pydantic models, but not with others see https://docs.pydantic.dev/latest/concepts/json_schema/#using-json_schema_extra-with-a-dict and 93f2620. I'll document this if msgspec also supports, see jcrist/msgspec#689.