Merge pull request 'add node os version' (#6) from add-node-version into main

Reviewed-on: #6
Reviewed-by: Stanislav_Kopp <stanislav.kopp@mail.schwarz>

ske-cluster/README.md

@@ -16,6 +16,7 @@ module "ske-cluster" {
       machine_type       = "c1.2"
       minimum            = "2"
       maximum            = "3"
+      os_version_min     = "4230.2.0"
       availability_zones = ["eu01-3"]
     }
   ]

ske-cluster/variables.tf

@@ -15,6 +15,7 @@ variable "ske_node_pools" {
     machine_type       = string
     minimum            = number
     maximum            = number
+    os_version_min     = string
     availability_zones = list(string)
   }))
 }