feat: Add RKE2 as alternative Kubernetes distribution for service cluster

[j0hnL]

Summary

Add support for deploying RKE2 (Rancher Kubernetes Engine 2) as an alternative to vanilla Kubernetes (kubeadm) for the service cluster. Users can choose the distribution via the new k8s_distro field in omnia_config.yml.

How to use

1. In input/omnia_config.yml, set k8s_distro: "rke2" in the service_k8s_cluster block
2. In input/software_config.json, replace service_k8s with service_rke2 in the softwares list
3. Run the pipeline as normal (local_repo.yml → build_image_x86_64.yml → discovery.yml)

Configuration changes

• Add k8s_distro field to service_k8s_cluster in omnia_config.yml (default: kubeadm)
• Update omnia_config.json schema to validate k8s_distro enum (kubeadm/rke2)
• Expand k8s_cni enum to include canal, cilium, flannel (RKE2-supported CNIs)

Pipeline integration

• discovery.yml: Enable service_k8s tag when service_rke2 is in software_config.json
• include_software_config.yml: Detect service_rke2 and set service_rke2_support fact
• validate_software_config_json.yml: Handle service_rke2 arch and version detection
• common_validation.py: Accept service_rke2 for cluster validation
• image_package_collector.py: Dynamically select service_rke2.json for image builds
• k8s_config/main.yml: Branch NFS setup based on k8s_distro
• configure_cloud_init_group.yml: Select RKE2-specific templates when k8s_distro=rke2

New files

• 3 RKE2 cloud-init templates (first server, additional server, agent)
• create_rke2_config_nfs.yml for RKE2-specific NFS directory setup
• service_rke2.json package definitions for RHEL 10.0 x86_64

Key differences from kubeadm path

• RKE2 uses built-in containerd (no CRI-O)
• RKE2 manages CNI lifecycle (calico/canal/cilium/flannel)
• Token-based cluster join instead of kubeadm certificates
• kube-vip deployed as RKE2 static pod manifest
• RKE2 registries.yaml for Pulp mirror integration
• Port 9345 for RKE2 supervisor API

Backward compatibility

Existing kubeadm deployment is completely unaffected when k8s_distro=kubeadm (the default). All branching logic only activates for rke2.