Add support for downloading from Unity Catalog volumes

[maddiedawson]

Description of changes:

This change allows users to upload data to and download data from Databricks Unity Catalog.

To configure authentication using mcli, user would run:

mcli create secret env DATABRICKS_HOST=...
mcli create secret env DATABRICKS_TOKEN=...

Env vars consistent with https://databricks-sdk-py.readthedocs.io/en/latest/authentication.html

Issue #, if available:

STR-116

Merge Checklist:

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[karan6181]

Overall looks great. Few minor comments:

• Can you also add the similar functionality in upload.py which basically uploads the shard files in UC during dataset conversion? You can look at PR 311 and 265 for reference.
• Can you also add a unit test for the same in test_download.py and test_upload.py ?
• Can you also update the documentation with UC Volume section on how user would provide a credentials ?

Thanks!

[maddiedawson]

Overall looks great. Few minor comments:

• Can you also add the similar functionality in upload.py which basically uploads the shard files in UC during dataset conversion? You can look at PR 311 and 265 for reference.

Done

• Can you also add a unit test for the same in test_download.py and test_upload.py ?

Done

• Can you also update the documentation with UC Volume section on how user would provide a credentials ?

Done

Thanks!

[karan6181]

The PR looks good to me, Can you rebase the PR and then fixed the lint issue which I mentioned in PR 362? Thanks!