azure transfer driver modeled on the s3 one

[petersilva]

Having a built-in driver for Azure, modelled on the S3 one recently provided, should allow sr3 user the ability to poll, post, and subscribe to resources made available on Microsoft cloud storage offerings. we have an example usage of azure here:

https://github.com/MetPX/sr3-examples/tree/main/cloud-publisher-azure

done using a plugin (there is a similar cloud-publisher-s3 as well.) but a native Transfer sub-class would be a lot more straight-forward to use.

[gcglinton]

Initial work for this is done in Issue1015_AzureTransferDriver branch.

I've been able to test most of the functionality directly with the class, but need to do more when run via sr3.

Unit testing is going to be very challenging, because there's no easy way to mock the Azure SDK, short of patching the methods, and statically catching/returning things.

[gcglinton]

This should now be complete, as #1051 has the last unit tests for the driver.

It still needs operational testing, but so does the S3 driver.