Better support for authentication with AAD tokens

[alexott]

This PR adds support for authentication using AAD tokens that could be obtained by different means:

• using azure-cli's az account get-access-token
• Service Principal - with client ID & secret
• azure managed identity assigned to Azure VM

Support for AAD tokens enables use of databricks-cli in organizations that don't permit PATs

[savbace]

Do we expect the PR to be merged? I faced with a need to authenticate using Service Principal too.

[nfx]

We'll have a proper Databricks Python SDK that will support AAD auth, can't share the timelines. Stay tuned :)