Cluster Provisioning: allow to specify internal and external addresses

[fgiudici]

k3s and RKE2 allow to specify and external-ip-address for nodes (for instance to support the distributed/hybrid cluster scenario). Rancher Provisioning v2 supports the CATTLE_ADDRESS and CATTLE_INTERNAL_ADDRESS agent variables for customizing the internal and external IP addresses of k3s and RKE2. Those agent variables are not honored when provisioning is performed via Elemental (see #841) and there is no way at present to allow specifying external addresses with Elemental.

This issue is about introducing a way for the users to specify internal and external addresses for k3s and RKE2 when provisioned via Elemental (see https://github.com/rancher/elemental-operator/issues/841#issuecomment-2377396551 for details on why this is not working).