Add support for tier0 and tier5k to create boot images

[kishen-v]

Changes:

• Tier0 and Tier5k are available in select regions and instances. This change enables users to pick from two additional choices - Tier0 and Tier5k, along with the existing Tier1 and Tier3 storage tiers to create boot images.
• Validation of tier availability in a given region, using the cloud instance ID.

Tier0

Tier5k

Invalid storage tier.

./pvsadm image import --workspace-id <> --object <> --pvs-image-name <>--pvs-storagetype tier54 --bucket-region jp-tok --watch -v4 -b <>

E0821 11:24:15.770645   58796 main.go:26] provide valid StorageType. Allowable values are [tier3 tier1 tier0 tier5k]

[ppc64le-cloud-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kishen-v, mkumatag

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