Make CloudDisk methods compatible with alphaDisk

[amacaskill]

What type of PR is this?

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/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test

/kind feature

/kind flake

What this PR does / why we need it:
This PR makes CloudDisk methods compatible with alphaDisk. This is a follow up PR #1524, which added the capability to use the GCE Alpha API to create zonal disks when Storage Pools is enabled.

This PR also adds the CloudDisk method GetEnableStoragePools(), which will be used in a follow up PR in metrics.GetMetricParameters() to add another dimension enable_storage_pool to the already existing csidriver_operation_errors metric to track the CSI operations error rate while using Storage Pools.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[amacaskill]

/assign @mattcary

[mattcary]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amacaskill, mattcary

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