Add behavior to compute external path from root/catalog/schema/identifier

[benc-db]

Describe the feature

Provide a mechanism so that tables are written to external paths that match the structure in Databricks

Describe alternatives you've considered

Asked about the possibility of encoding this in yaml files with variables, not sure if this is currently possible

Additional context

The lack of this is currently a big pain in testing, where sometimes UC complains that a table already exists at the location (since we only use table identifier today).

Who will this benefit?

Anyone that uses external locations and does non-trivial work