[Bug]: nullable properties not supported in openapi doc

### What happened?

It looks like the OpenAPI document does not honor nullability of properties despite this being supported in OpenApi 3.1:

https://www.openapis.org/blog/2021/02/16/migrating-from-openapi-3-0-to-3-1-0

See https://github.com/ErikEJ/EFCorePowerTools/issues/2597

### Version

1.2.11

### What database are you using?

Azure SQL

### What hosting model are you using?

Local (including CLI)

### Which API approach are you accessing DAB through?

REST

### Relevant log output

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Comienza reproduciendo el documento REST OpenAPI para nullable properties con respecto a la versión 1.2.11, utilizando Azure SQL y la referencia enlazada de OpenAPI 3.1 para comparar. Rastrea dónde representa el documento generado la nullability de las properties y, a continuación, verifica que el schema resultante la conserve y coincida con el comportamiento esperado de OpenAPI 3.1.

Escrito por el modelo de indexación a partir del texto del issue.