Better standardize Task.reasonReference by formalizing (but not limiting) the current scenarios

PAS Claim  constrained to the preauthorization use case and cannot be used for other use cases such as claims attachments or audits and the t he commenter suggests.  Will reference the FHIR base claim resource as it is defined in HRex.   re:  Formalizing the described scenarios into specific use-cases:   Document in the IG: The intent of the rewritten IG was not to enumerate specific use-cases and provides examples. For this IG we focus the existing examples on simple scenarios  to illustrate the different approached for exchanging Clinical data.  Instead we plan to create "Clinical Data Exchange- Supplemental Guide(s)"  which will consist of use case examples. And reference where they will resolve.