Add support for OAuth authentication on AWS

[alexott]

Databricks now supports:

• OAuth for Databricks service principals: https://docs.databricks.com/dev-tools/auth.html#oauth-m2m-auth
• OAuth for Databricks users: https://docs.databricks.com/dev-tools/auth.html#oauth-u2m-auth (need to validate if it could be done for Splunk extension)