[#52755345] Implements the HdfsDataset, and an API endpoint for creating them.
[#52755345] Re-records VCR search cassettes to include HdfsDatasets
[#52755345] HDFS Datasets can be created with a File Mask and appear in the data tab of given Workspace.

- Many places make explicit exceptions for HDFS Datasets
- hdfs_dataset icon included
- dynamic dataset respects "HDFS" entitySubtype
- HdfsDataset sets its own entitySubtype & overrides Dataset.dataSource()
- datasetLocation string generation respects differences between HDFS & DB datasets
- datasetItemView can display HDFS Datasets
Re-record VCR cassettes to reflect new Dataset population