[WIP] feat: support changing cachingMode through VolumeAttributeClass

[andyzhangx]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds support for changing cachingMode via VolumeAttributeClass by validating the parameter in ControllerModifyVolume and updating the disk's caching mode on the VM in-place.

How it works

cachingMode is a VM-level data disk attachment property. When modified via VolumeAttributeClass:

1. ControllerModifyVolume validates the new cachingMode value
2. Enforces constraints: disks >= 4 TiB only support None; PremiumV2_LRS only supports None
3. If the disk is currently attached to a VM, calls UpdateDiskCachingMode which:
   • Finds the node the disk is attached to via disk.ManagedBy
   • Gets the disk's current LUN
   • Issues an AttachDisk call with the existing LUN and new cachingMode to update the VM
4. If the disk is not attached, the update is a no-op — the new cachingMode will be applied on next attach via PV volumeAttributes

Changes

• azure_controller_common.go: Added UpdateDiskCachingMode method on controllerCommon
• controllerserver.go: Added cachingMode validation and update logic in ControllerModifyVolume
• controllerserver_test.go: Added 4 unit test cases (3 valid modes + 1 invalid)

Example VolumeAttributeClass

apiVersion: storage.k8s.io/v1beta1
kind: VolumeAttributesClass
metadata:
  name: caching-readonly
driverName: disk.csi.azure.com
parameters:
  cachingMode: ReadOnly

Which issue(s) this PR fixes:

Fixes #3471

Special notes for your reviewer:

• Supported cachingMode values: None, ReadOnly, ReadWrite
• For attached disks, the change is applied in-place via VM update (no pod restart required)
• For unattached disks, the new cachingMode takes effect on next attach

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx

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[k8s-ci-robot]

@andyzhangx: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-azuredisk-csi-driver-e2e-capz	7d82151	link	true	/test pull-azuredisk-csi-driver-e2e-capz

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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