Add Oauth authentication for Azure AD SSO

[amandoabreu]

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Not sure if the design pattern is the best. After getting to a certain point I did wish I had separated some stuff away from SnowflakeClient.cs into some sort of Authenticator class. Tests just mock the AzureAd response and make sure the new AzureAdAuthInfo can be instantiated. Integration tests are hard as it requires the specific setup.