request: `utoipa` feature

[dsgallups]

Hello! I'm working on a little hobby project at the moment. I use the utoipa crate to generate my openapi spec. Though GeoJSON is a common type in typescript syntax, I am using some of the specific subsets of geojson in this crate.

This feature request might be controversial, but I'll nonetheless send up a PR to gauge that response. 🙂