fix: add backup retention

Mainly to get rid of the always changing to null values

k8s.tf

@@ -109,6 +109,12 @@ resource "kops_cluster" "k8s" {
           encrypted_volume = true
         }
       }
+
+      manager {
+        backup_retention_days = var.backup_retention
+        listen_metrics_ur_ls  = []
+        log_level             = 0
+      }
     }
   }
 

vars.tf

@@ -262,3 +262,9 @@ variable "control_plane_prefix" {
   default     = "control-plane"
   description = "Prefix of control plane instance groups"
 }
+
+variable "backup_retention" {
+  type        = number
+  default     = 90
+  description = "Backup retention of etcd data in days"
+}