[Feature request]: Integer as type discriminator

[vanillajonathan]

Is your feature request related to a specific problem? Or an existing feature?

I am using integers as type discriminator.

[JsonPolymorphic]
[JsonDerivedType(typeof(Cat), (int)PetKind.Cat)]
[JsonDerivedType(typeof(Dog), (int)PetKind.Dog)]
public class BaseModel
{
    public string Name { get; set; }
}

The SelectDiscriminatorValueUsing method can only return a String.

builder.Services.AddSwaggerGen(c =>
{
    c.UseOneOfForPolymorphism();
    c.SelectDiscriminatorNameUsing((baseType) => "$type");
    c.SelectDiscriminatorValueUsing((subType) => subType.Name); // can only return String
});

Describe the solution you'd like

An overload for the SelectDiscriminatorValueUsing method that accepts a custom selector with the signature Func<Type, int> customSelector.

Additional context

No response

[martincostello]

Assuming that arbitrary type descriminiators are valid in OpenAPI, then that sounds reasonable. However we'd want to make it generic if possible (int, bool, etc.), rather than only supporting either an int or a string.