Need to Introduce worker_node_count Variable in Cluster Spec

In our current setup, the cluster spec includes a variable node_count which represents the total number of nodes in the cluster (i.e., control plane + worker nodes). However, several use cases require the ability to distinguish between control plane and worker node counts.

A specific use case (issue: #2489 (closed)) involves restricting the scheduling of KubeVirt VMs to only worker nodes, which requires knowing the exact count of worker nodes.

Proposed Enhancement: Introduce a new variable under .Values.cluster named worker_node_count which:

Computes the sum of replicas across all machine_deployments.

Example Use Case:

Define KubeVirt VM placement policies (like nodeSelector, affinity, etc.) based on whether worker_node_count > 0