Azure - customize data-disks names

_This issue was originally opened by @vanbukin in https://github.com/hashicorp/packer/issues/7853 and has been migrated to this repository. The original issue description is below._

---
Feature request
Affected versions: 1.4.2

As I see [here](https://github.com/hashicorp/packer/blob/v1.4.2/builder/azure/common/template/template_builder.go#L243) - there is no way to customize [additional data-disk](https://www.packer.io/docs/builders/azure.html#disk_additional_size) name when I build images in Azure. So if I don't want to use temporary resource group each time (for cost management purposes) - I can't run multiple parallel images builds at the same resource group, because data disk with same name may already exists (it always be `datadisk-1`, `datadisk-2` and so on)

So, please add ability to customize that name - maybe suffix or prefix, or something other.

Start with builder/azure/common/template/template_builder.go at the linked data-disk handling area, then review the Azure builder documentation for disk_additional_size. Determine how a configurable data-disk name component should be exposed and applied; done means parallel builds can use distinct additional data-disk names in the same resource group.

Written by the indexing model from the issue text.