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- Fixed call to isdir(), to run direct call to Azure container, instead of calling .ls on the directory
- Fixed call to isfile() to directly evaluate the file, insteading of calling ls on the directory
- Updated unit test for isdir
- Added DefaultAzureCredential as an authentication method. Activated if anon is False, and
no explicit credentials are passed. See authentication methods enabled [here](https://docs.microsoft.com/en-us/python/api/azure-identity/azure.identity.defaultazurecredential?view=azure-python).
- Updated initiate_upload() method to allow overwriting a blob if the credentials do not have delete priveleges.