Object endpoint for DRS bundles - local directories as bundles

[jb-adams]

Currently, the /objects/{object_id} endpoint is only configured to load a DRSObject representing a single blob. This functionality should be expanded to handle bundles. In a local filesystem context, files map to DRSObject single blobs, whereas directories map to DRSObject bundles. For a given id mapping to a directory, the server app must traverse all subdirectories to all files, and format this as a DRSObject bundle.

This will likely lead to a revamp of our current data source registration model, as the current lookup based on regex has no mechanism to give the correct id for a file under a requested bundle