Unsupported type on complex unions can return a union of "UnsuportedType = UnsupportedType"

Problem/Motivation

Thanks to cruno for reaching out on slack

Steps to reproduce

Create entity reference field
Reference entity thats not exposed in GraphQL Compose
Disable "Simple entity unions"

Proposed resolution

Continue if union type sdl = UnsupportedType unions.

Remaining tasks

NA

User interface changes

NA

API changes

NA

Data model changes

NA