chore: bump terraform requirement to 0.13

Bump TF to 0.13 and remove old experiments.

examples/hcloud-k3s/versions.tf

@@ -0,0 +1,8 @@
+terraform {
+  required_providers {
+    hcloud = {
+      source = "terraform-providers/hcloud"
+    }
+  }
+  required_version = ">= 0.13"
+}

main.tf

@@ -1,13 +1,3 @@
-terraform {
-  required_version = "~> 0.12"
-  experiments      = [variable_validation]
-  required_providers {
-    http   = "~> 1.2"
-    null   = "~> 2.1"
-    random = "~> 2.2"
-  }
-}
-
 // Generate the k3s token used by all nodes to join the cluster
 resource "random_password" "k3s_cluster_secret" {
   length  = 48

versions.tf

@@ -0,0 +1,17 @@
+terraform {
+  required_providers {
+    http = {
+      source  = "hashicorp/http"
+      version = "~> 1.2"
+    }
+    null = {
+      source  = "hashicorp/null"
+      version = "~> 2.1"
+    }
+    random = {
+      source  = "hashicorp/random"
+      version = "~> 2.2"
+    }
+  }
+  required_version = ">= 0.13"
+}