Implement new API endpoints for browsing and retrieving artifact files

[keithmanville]

Implement required schemas, controllers, and services to achieve functionality for browsing and retrieving artifact files as defined in #574

The service layer implementation will need to make use of the mlflow client to list and retrieve artifact files.

Definition of Done:

• The implemented schemas and endpoints match the design documents
• The feature meets the functionality defined in Document new API endpoints for browsing and retrieving artifact files #574
• The client is updated to support the changes to artifacts
• Tests are implemented to cover new functionality
• All tests pass
• The feature is merged into dev