Related to FHIR#28909 for the base spec.

Related chat.fhir thread.

In order to support mapping CapabilityStatements to the ONC's CHPL listing, we should consider creating an extension on CapabilityStatement.  CapabilityStatement.software is currently 0..1 so it doesn't let a server indicate that it is in front of multiple products.

The simple solution is just a 0..* extension that lets you list a name and version.  If we want to get fancy, we could include an Identifier so we can reference the CHPL product ID directly.