Add more explicit Unity Catalog support

[danielbeach]

You can in theory, per the README you can describe tables in Spark with Unity Catalog and get the s3 uri and pass this into the tool. It would be good to add easier interface into running inside Unity Catalog.

[josiahjohnston]

I did a DIY solution to that last week in Databricks for managed UC tables, getting listings of active files for Delta and file-level indexes (aka statistics). I only got it to work on some classic clusters where I had set up AWS credentials for direct S3 access with tools like boto3, s3fs. Databricks easy access via roles, volumes, or spark tools for reading the _delta_logs directory all failed.
To work on serverless, I think I'd need to change my implementation to pull credentials from dbutils secrets and explicitly pass into the boto3/s3fs client(s). But all of that does make the library less usable & portable to typical clusters and installs. But should be fine for probes from my laptop with AWS credentials configured in a standard way..