Named schema support in Swagger & OpenAPI for Spec

[opqdonut]

Currently, all spec schemas are inlined at the use site when generating Swagger & OpenAPI docs.

It would be nice to generate Swagger :definitions and OpenAPI :components :schemas like we do for Malli refs/vars. See #673 .

For Malli, it's easy to control what gets a named schema by using the schema structure. What do we want for spec? A named schema for each s/def?