XML attribute fixes

[joelrosario]

What:

1. When an XML node referred to another XML node, the attributes from the referred XML node were dropped. It was built this way when adding WSDL support.
2. If an attribute was declared in the OpenAPI spec but not added to the required list, it was still considered mandatory, though it should have been considered optional.

Checklist:

• [ ] Documentation added to the README.md OR link to PR on https://github.com/specmatic/specmatic-documentation
• [x] Tests
• [ ] Sonar Quality Gate