terraform: Rename firewall base rule to `k8s-node`

terraform/firewall.tf

 # https://docs.k8s.io/latest/installing/installing_platform_agnostic/installing-platform-agnostic.html#installation-network-connectivity-user-infra_installing-platform-agnostic
-resource "hcloud_firewall" "k8s-base" {
-  name = "k8s-base"
+resource "hcloud_firewall" "k8s-node" {
+  name = "k8s-node"
   apply_to {
     label_selector = "k8s.io/node=true"
   }