Enable Boot Diagnostics with Managed Storage Account

[j7lloyd]

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Description

As recommended by Microsoft, using a managed storage account for boot diagnostics provides significant performance improvements when creating Azure VMs, by eliminating the need to create a separate storage account for boot diagnostics data.

Additionally, it simplifies management by removing any consideration for manually cleaning up storage accounts that store the serial console log and screenshot file after the VM build is completed.

Potential configuration

The ideal solution would be to implement it the same way it is done for a Virtual Machine in Terraform, using an optional block: https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/windows_virtual_machine#boot_diagnostics

boot_diagnostics {
  storage_account_uri = null
}

NOTE: Passing a null value will utilize a Managed Storage Account to store Boot Diagnostics.

Potential References

I was hoping this could be as simple as implementing a conditional if statement to make the following property (StorageUri) optional:

packer-plugin-azure/builder/azure/common/template/template_builder.go

Line 539 in 93909bc

resource.Properties.DiagnosticsProfile.BootDiagnostics.StorageUri = &stg