Support custom naming for GenericModel subclasses

[dmontagu]

Feature Request

Right now, it is not easy to use a custom naming scheme for a generic models. But I think this could be useful in some cases.

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I recently faced this problem when I realized that the generated schema for List[Optional[T]] types doesn't actually mark the value type as optional (strangely/sadly I think there isn't currently a well-supported way to do this under OpenAPI).

My workaround was to create a wrapper class for optionals:

class OptionalWrapper(GenericModel, Generic[T]):
    value: Optional[T]

But I wanted to override the cls.__name__ since that is used by FastAPI when generating the openapi spec. (For example, I wanted to see OptionalInt instead of OptionalWrapper[int].)

Given how small a code change this requires, I think it should be reasonable, but I figured I'd create an issue for discussion just in case.