Features
* Make DistributedConfig Extensible
* support training for JumpStart model references as part of Curated Hub Phase 2
* Allow ModelTrainer to accept hyperparameters file
Bug Fixes and Other Changes
* Skip tests with deprecated instance type
* Ensure Model.is_repack() returns a boolean
* Fix error when there is no session to call _create_model_request()
* Use sagemaker session's s3_resource in download_folder
* Added check for the presence of model package group before creating one
* Fix key error in _send_metrics()