Add warning about Terraform AWS provider version

* Sync Terraform provider versions with those used internally

docs/flatcar-linux/aws.md

@@ -55,7 +55,7 @@ terraform {
     }
     aws = {
       source = "hashicorp/aws"
-      version = "4.5.0"
+      version = "4.20.0"
     }
   }
 }

docs/flatcar-linux/azure.md

@@ -52,7 +52,7 @@ terraform {
     }
     azurerm = {
       source = "hashicorp/azurerm"
-      version = "2.99.0"
+      version = "3.9.0"
     }
   }
 }

docs/flatcar-linux/digitalocean.md

@@ -55,7 +55,7 @@ terraform {
     }
     digitalocean = {
       source = "digitalocean/digitalocean"
-      version = "2.18.0"
+      version = "2.21.0"
     }
   }
 }

docs/flatcar-linux/google-cloud.md

@@ -56,7 +56,7 @@ terraform {
     }
     google = {
       source = "hashicorp/google"
-      version = "4.13.0"
+      version = "4.25.0"
     }
   }
 }