Allow access to template ClusterClass topology variables

[raafatseif]

User Story

As an operator, I would like to access topology variables to have better alignment with ClusterClasses and improve configuration

Detailed Description

This will allow easy access to the variables we already provide and help avoid metadata duplication for clusters deployed using ClusterClasses. The proposal for CAPI Addon Orchestration shows plans to build this feature. Is the work being tracked anywhere?

In a future iteration we might consider to leverage template variables in ClusterClass. If a HelmChartProxy is selecting clusters with a managed topology, then the Go template configuration can benefit from Cluster.spec.topology.variables, and from the strong typing/validation ensured by the variable schema defined in corresponding ClusterClass.

Anything else you would like to add:

Versions:
CAAPH Provider: v0.2.6
Kubernetes: v1.31.4+rke2r1

/kind feature