Support accelerator directive for Azure Batch

[bentsherman]

The accelerator directive is currently supported for AWS Batch, Google Batch, and Kubernetes. Azure Batch also has GPUs, so this directive should also work for Azure Batch.

Not sure yet how to implement it yet with the Azure Batch Java SDK. All I found so far is the GpuResource class. @abhi18av do you have any idea how we would support GPU requests here? I don't know if there are specific GPU-enabled instance types, or if we can just attach a GPU to any instance or what.

In any case, I think we can map the accelerator type to the GpuSku enum:

final accel = task.config.getAccelerator()
new GpuResource()
    .withCount( accel.getRequest() )
    .withType( GpuSku.fromString(accel.getType()) )

So an example request would look like:

accelerator 1, type: 'V100'