Add utoipa schema support

[bjchambers]

This would parallel the JsonSchema support provided with the schemars feature flags. Specifically, doing the same thing but for utoipa for use in OpenAPI schemas.

[jonasbb]

Hi, thank you for the suggestion. I haven't heard of that crate yet. This can fit into this crate, since the schemars support is already here.

I will probably not implement this myself soon, but I am happy to review and accept a PR for this.