fix(aide-axum): properly infer response descriptions

[snejugal]

subschema_for is likely to return just a reference to a schema, and it will not contain any metadata. However, axum::Json (and axum::Form) do not try to resolve the reference before extracting schema description, and that leaves blank response descriptions in rendered docs. So I added a call to resolve_schema to ensure that we get the actual schema before extracting its description.

[JakkuSakura]

LGTM