Support intended usageContext for included artifacts

This issue is related to and implements the CRMI specification change described here: https://jira.hl7.org/browse/FHIR-53237

There is a need to establish context-specific usage context information for specification libraries. For example, value sets included in a public health reporting specification need to be able to specify the priority and focus of the value set. However, this information cannot always be provided on the value set itself because a) it is context-specific (i.e. it is an aspect of the appearance of the value set in the specification, rather than intrinsic to the value set itself) and b) it needs to be specified for value sets that are outside the authoring control of the specification editors.

To support this use case, consider defining:

1. An "intended usage context" extension:
   crmi-intendedUsageContext 0..* UsageContext, usable on relatedArtifact
   Definition: An intended usage context associated with the dependency on which it appears. When the dependency is packaged, this usageContext will be applied to the packaged artifact.
2. Add this extension as allowed on dependencies in the Manifest Library profile.
3. Document this use case and feature as a new section in the Packaging topic.