Derive VPC zones from VPC region instead of PowerVS region.

[kishen-v]

What this PR does / why we need it: This PR contains changes to derive the VPC zone from the VPC region, compared to the zone derived from PowerVS region. This mitigates errors/conflicts arising where the VPC zone is different from the PowerVS zone, causing a mismatch in the CIDR.

Tests: The change has been tested where the compute infrastructure is provisioned in jp-osa, while the VPC subnet infrastructure was provisioned in jp-tok. The was available for use post completion of deployment.

A similar exercise was done to provision both Compute and VPC subnet in jp-osa.

Which issue(s) this PR fixes : Fixes #1817

Special notes for your reviewer: Please let me know if there are other scenarios to be covered before the changes can be merged to main.

/area provider/ibmcloud

Release note:

Derive VPC zones from VPC region instead of PowerVS region.

[k8s-ci-robot]

Hi @kishen-v. Thanks for your PR.

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[kishen-v]

cc : @Karthik-K-N @Amulyam24

[Amulyam24]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes-sigs/cluster-api-provider-ibmcloud/blob/main/OWNERS)~~ [Prajyot-Parab] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment