Support accelerator directive for Azure Batch

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'

Start by tracing the existing accelerator support for AWS Batch, Google Batch, and Kubernetes, then inspect how the Azure Batch Java SDK represents GPU resources and instance types. Determine whether GpuResource and GpuSku apply to Azure Batch, and define the supported mapping for an example such as accelerator 1, type: 'V100'. Done means Azure Batch accepts and provisions the requested accelerator consistently with the other backends.