chore: recommend OpenTofu CI/CD component in script when using tofu

src/bin/gitlab-terraform.sh

@@ -15,8 +15,14 @@ terraform_is_at_least() {
 # if tofu is present, 1 if it's not
 using_open_tofu() {
   # If tofu is on the path, we're using tofu, not terraform.
-  [ "$(which tofu)" ]
-  return $?
+  if [ "$(which tofu)" ]; then
+    echo "It looks like you are using OpenTofu."
+    echo "Please migrate to the OpenTofu CI/CD component: https://gitlab.com/components/opentofu."
+    echo "The terraform-images project won't receive any OpenTofu related updates."
+    return 0
+  else 
+    return 1
+  fi
 }
 
 # Evaluate if this script is being sourced or executed directly.