Refactor: Move get_value_descriptions_from_cadsr() out of GdcImporter

[joeflack4]

Description

There's nothing about this function that is specific to GDC. In fact, PDC even uses it. It ought to be moved to another class, probably more likely, module.

Additional info

Important considerations before making this change

Upon examination in the debugger, I'm seeing that there were no values returned form this for any attributes in PDC. All of them returned None. I'm wondering if this is (a) a mistake and this should not have been used in the first place, or (b) not a mistake, and something missing on the server end; maybe somewhere that Harold and Dazhi left off. Perhaps the relevant values for PDC data was intended to be imported into the hot ecosystem FHIR server?