Boot diagnostics storage account configuration

* `infra_map`, `subscription_infra_map`, and `infra_map_vm_set` all support the `enable_boot_diagnostics` property which, by default, is toggled off. An Azure-managed storage account is used to store diagnostics.
* Wherever the `enable_boot_diagnostics` property is found:
* In `infra_map_vm_set`, a variable needs to be added that provides a storage account ID.
* In `subscription_infra_map` and `infra_map_vm_set`, a property needs to be added for each VM set that references a storage account (by `storage_account_name`) defined in the `storage_accounts` map variable.

> [!NOTE]
> This task is dependent on completion of `var.storage_accounts` support