feat(terraform): Ensure ephemeral disks are used for OS disks

[tdefise]

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Description

Fixes #5583

New/Edited policies (Delete if not relevant)

Description

Temporary data can contain sensitive data at some points, by using ephemeral disks, we ensure that data written to OS disk is stored on local VM storage and isn't persisted to Azure Storage

Azure automatically replicates data stored in the managed OS disk of a virtual machine to Azure storage to avoid data loss in case the virtual machine needs to be relocated to another host.
Generally speaking, containers are not designed to have local state persisted to the managed OS disk, hence this behavior offers limited value to AKS hosted while providing some drawbacks, including slower node provisioning and higher read/write latency.
Ephemeral disks allow us also to have faster cluster operations like scale or upgrade due to faster re-imaging and boot times.

More information can be found here

Fix

Set the disk type to "Ephemeral"

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[JamesWoolfenden]

LGTM

[gruebel]

thansk again 🍻