Add cert-manager and let's encrypt to the k8s-cluster

This change contains a new module which will be applied after the
kubernetes-cluster has been created. It will install the cert-manager in
it and add let's encrypt as a ClusterIssuer to the cluster. That setup
allows me to simply issue certificates for all services in the cluster.

k8s/versions.tf

@@ -0,0 +1,22 @@
+terraform {
+  required_providers {
+    helm = {
+      source  = "hashicorp/helm"
+      version = "3.0.2"
+    }
+    kubernetes = {
+      source  = "hashicorp/kubernetes"
+      version = "2.38.0"
+    }
+  }
+}
+
+provider "helm" {
+  kubernetes = {
+    config_path = "~/.kube/config"
+  }
+}
+
+provider "kubernetes" {
+  config_path = "~/.kube/config"
+}