Support tier0 and tier5k as storage type

[yussufsh]

Is your feature request related to a problem? Please describe.
We are unable to use the below new storage types due to hard validation:

tier0    Tier0 - 25 iops/gb
tier5k   Tier5k - 5000 fixed iops

Describe the solution you'd like in detail
Disk creation should not fail with invalid PowerVS VolumeType tier5k error message when using the new storage type.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
List of storage types available: https://cloud.ibm.com/docs/power-iaas?topic=power-iaas-about-virtual-server#storage-tiers

o/p via CLI:

# ibmcloud pi storage-types
Listing storage types in region tok04...
Type     Description
tier0    Tier0 - 25 iops/gb
tier1    Tier1 - 10 iops/gb
tier3    Tier3 - 3 iops/gb
tier5k   Tier5k - 5000 fixed iops

[k8s-triage-robot]

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/lifecycle stale

[yussufsh]

/remove-lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough contributors to adequately respond to all issues.

This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

You can:

• Mark this issue as fresh with /remove-lifecycle stale
• Close this issue with /close
• Offer to help out with Issue Triage

Please send feedback to sig-contributor-experience at kubernetes/community.

/lifecycle stale

[mkumatag]

/remove-lifecycle stale