Support for schema containing ZodIntersection or ZodDefault #9

Thanks for this library so far 🎉

Driven by the same error as reported in #8, I analyzed why my schema was failing.

I debugged and found out that the generator currently throws an error if the instance it expects to be a zod-object does not exactly match one of the tested types (ZodObject, ZodVoid or ZodOptional): https://github.com/dtinth/openapi-trpc/blob/main/src/generate.ts#L141

I'd like that list to be extend to include ZodIntersection and ZodDefault as well - I use them in my schema, and I didn't run into a problem when just adding it to the code of this package.

If you see anything I might have overlooked, please tell me and I'm happy to test it more.