We're seeking an exception for not deriving from US Core ServiceRequest

1. Our IG is based on 3.1.1, and ServiceRequest isn't there.
2. We're largely aligned with compliant with US Core.  The only exceptions are that we don't have MustSupport on intent and don't require category.  Neither are needed for our use-case.  However, if we were formally deriving, we'd include them given that the EHRs would always have them.  We'd just indicate that the payers would be free to ignore.