fix: Use existing 'infra' SSH key instead of creating new one

terraform/ssh.tf

@@ -2,7 +2,6 @@ data "local_file" "ssh_public_key" {
   filename = pathexpand(var.ssh_public_key)
 }
 
-resource "hcloud_ssh_key" "cluster" {
+data "hcloud_ssh_key" "cluster" {
-  name       = "${var.cluster_name}-ssh-key"
+  name = "infra"
-  public_key = data.local_file.ssh_public_key.content
 }