Add Troubleshooting Guide and Improve Installer Script Variable Validation

[taliandre49]

This PR enhances the installer script to improve usability and reduce common setup issues.

Key Updates:

• Added clearer validation and guidance for required environment variables (IBMCLOUD_API_KEY, RELEASE_VER, etc.)
• Introduced detailed echo messages explaining defaults and how to override them (e.g., RHCOS version).
• Clarified the default RHCOS image version (8.3) and provided explicit guidance on changing image versions.
• New troubleshooting.md under docs/
  • documents common OpenShift on PowerVS installation issues, their causes, and step-by-step resolutions.
  • Covers Terraform state issues, Bastion OS compatibility, reinstallation conflicts, remote-exec failures, LPAR health issues, and missing image errors.
  • References verified solutions and relevant IBM/PowerVS documentation for easier user debugging.

Testing:

• Verified successful execution by running the installer script end-to-end after these updates.

Context:

These changes address issues observed when users and/or customers encounter missing or outdated image references during installation. The improved checks and messages help users identify configuration gaps earlier and adjust environment variables accordingly.

[ppc64le-cloud-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: taliandre49
Once this PR has been reviewed and has the lgtm label, please assign yussufsh for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ppc64le-cloud-bot]

@taliandre49: PR is not mergeable.

The PR state is: blocked

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ppc64le-cloud-bot]

Welcome @taliandre49! It looks like this is your first PR to ocp-power-automation/openshift-install-power 🎉