Credential passthrough readme

[shervyna]

Purpose

Create readme for credential passthrough in the databricks folder. Renamed dataset-versioning folder to dataset_versioning.

Does this introduce a breaking change?

• [ ] Yes
• [x] No

Author pre-publish checklist:

• [ ] Added test to prove my fix is effective or new feature works
• [x] No PII in logs
• [x] Made corresponding changes to the documentation