Add new value to version enum

[baywet]

The new 3.2 version needs to be added to the existing OpenAPIVersion enum

As part of this change, we also need to add a "SerializeAsV32" method to this interface (and update implementations).
https://github.com/microsoft/OpenAPI.NET/blob/main/src/Microsoft.OpenApi/Interfaces/IOpenApiSerializable.cs

This will probably be the only actual "breaking change" of all this work, but we can address/retro-fit that during the final review process.