merge external / native composition configuration option

These two elements are either/or, we need to merge them into something that makes it more obvious that you can either use our composition "native federation or apollo legacy" or "external composition". Maybe incorporating a toggle or tabs etc.

<img width="1220" height="513" alt="Image" src="https://github.com/user-attachments/assets/c38e41e7-10e3-4c46-9c7a-1969e3835319" />