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

Background Task.reasonReference and Task.reasonCode are 0…1 MS Changes 1. make Task.reasonReference.identifer 0…1 MS Add a comment to the element: Most payer systems will not expose their claim and prior authorization records as a FHIR resource. They will provide a unique business identifier for the claim or prior authorization using  Task.reasonReference.identifier .  This could be a payer-assigned or provider-assigned identifier which  SHOULD  be communicated in Task.reasonReference.identifier.type  using the FILL for the payer and PLAC for the provider. 2. update examples to use claim identifiers (and other business identifiers as well) to reflect the more likely usage. 3. The intent of this IG to provide a general approach illustrating the different approaches with a simple scenarios and representative examples. We will be adding the Attachments Use Case  as a specific use case. But we plan to create “Clinical Data Exchange- Supplemental Guide(s)” which will consist of the other use case examples. 4.  In the general case the  CDex Task Data Request Profile will not reference a specific Claim or Coverage profile.  For a specific use case, however the reasonreference may indeed reference a profile.