LPS-33805 Path parameter from StagedModelDataHandler --> please read comments

Hey Brian,

This change set has been reviewed by Mike Han (@mhan810) as well. He had only one concern, casting the StagedModel to ClassedModel, since the StagedModel is not extending the ClassedModel (nor the AuditedModel or GroupedModel).

As we discussed all entities that will be StagedModels are implicitly be ClassedModels too according to how the service builder works (model.ftl) although this is still a risk for class casting problems. We've agreed to eliminate this risk, and based on our conversation with Mike, I've added two new commits to the PR changing the AuditedModel to explicitly extend ClassedModel (will affect GroupedModel and StagedModel eventually).
The reason I haven't merged the commits together is to keep track of why it has been changed.

Thanks,

Máté

cc-ing also: @KocsisDaniel