Add Opt-In Support for Major OpenShift Version Upgrades via Terraform

[vburckhardt]

Description

Context:
There is a need to support major OpenShift version upgrades (e.g., 4.12 → 4.13) via Terraform. Currently, the kube_version field is included in lifecycle.ignore_changes, which prevents this. While this behavior is intentional to avoid drift due to IBM-managed patch updates, some users manage major upgrades manually and require Terraform to reflect those changes.

Introduce an opt-in mechanism in the module by doing the following steps:

• Add a new resource variant that excludes lifecycle.ignore_changes on kube_version.
• This variant should be activated only when explicitly requested by the user (e.g., via a module input variable).
• The default behavior of the module must remain unchanged: users will continue to receive the resource with ignore_changes enabled unless they opt in.
• Document the need for a one-time terraform state mv to migrate existing clusters to the new resource. Document also the need to regularly run terraform refresh to accommodate patch changes managed by IBM.

Impact:

• Enables users with specific operational models to manage major version upgrades via Terraform.
• Maintains safety defaults for all other users.
• Requires manual state migration per cluster for those opting in.