[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

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