Update language around ConceptMap properties and additionalAttributes

Replace the text in https://build.fhir.org/conceptmap.html#bnc with this (the changes are in red, the second set of 2 bullets replaces a single bullet in the current text) A number of metadata fields have been added (same as  CodeSystem  and  ValueSet ) source  and  target  were renamed to  sourceScope  and  targetScope  for clarity ConceptMap.group.element.target.equivalence  has been renamed to  ConceptMap.group.element.target.relationship  for clarity, and the set of relationship codes has simplified, and the code  umatched  has been moved to the  noMap  element ConceptMap.group.element.target.property  has been added to support providing additional details about the relationship between source and target. Like with  CodeSystem  and  ValueSet , properties are defined using  ConceptMap.property ConceptMap.group.element.target.dependsOn.property  was renamed to  ConceptMap.group.element.target.dependsOn. attribute  to clarify that these are not properties of the mapping, but additional attributes of the source or target content. The data type was changed from  url  to  code  which references  ConceptMap.additionalAttribute  to allow for a more concise representation, along with documentation ConceptMap.group.element.valueSet was added to facilitate mapping all concepts from a source value set   ConceptMap.group.element.target.valueSet has been added to facilitate mapping to each concept in a target value set relationship  and  valueSet  have been added to the  unmapped  element and some other clarifications have been made