Improvements to allow scripts to run locally

[andrewluotechnologies]

A few improvements that allow this script to be used both in Fabric and locally:

• Allow user to pass in a credential object instead of requiring the user to use a service principal
• Use local filesystem - the code already uses the /lakehouse mount when importing, I think it makes sense to keep it consistent. Additionally, if running this locally you can use your local storage with no dependency on Azure storage
• Don't prepend _ when prefix is empty