Support retrieving access tokens from IMDS

Since it appears that Active Directory is the recommended way of controlling access to Azure Storage, it would be useful if azure-storage-python, when running on an Azure Virtual Machine, supported automatically retrieving access tokens from the Azure Instance Metadata Service (IMDS).

I'm willing to take a stab at implementing this functionality if it is something that would be accepted. The biggest question in my mind is - what would the API for enabling this mode look like in the constructor for, say, BaseBlobService.

Comienza con el constructor de BaseBlobService y el flujo de tokens de acceso de Azure Instance Metadata Service (IMDS) descrito en el issue. Determina cómo debe habilitarse este modo y cómo deben recuperarse los tokens al ejecutarse en una Azure Virtual Machine; se considera terminado cuando la API y la implementación admiten el acceso de Active Directory a Azure Storage.

Escrito por el modelo de indexación a partir del texto del issue.