[Doc] authentication_mode doc update (#2788)

[Doc] authentication_mode doc update

Summary of the Pull Request
Updating doc regarding latest changes for authentication_mode attribute
PR Checklist

 Refers to: #2784
 Tests added/passed.
 Documentation updated.
 Schema updated.
 Release notes added.

Reviewed-by: Artem Lifshits

docs/resources/cce_cluster_v3.md

@@ -182,8 +182,14 @@ The following arguments are supported:
 
 * `eni_subnet_cidr` - (Optional) Specifies the ENI network segment. Specified when creating a CCE Turbo cluster. Changing this parameter will create a new cluster resource.
 
-* `authentication_mode` - (Optional) Authentication mode of the cluster, possible values are `rbac` and `authenticating_proxy`.
-  Defaults to `rbac`. Changing this parameter will create a new cluster resource.
+* `authentication_mode` - (Optional) Cluster authentication mode.
+  * Clusters of Kubernetes v1.11 and earlier
+    Possible values: `x509`, `rbac`, and `authenticating_proxy`
+  * Clusters of Kubernetes v1.13 and later
+    Possible values: `rbac` and `authenticating_proxy`
+
+  Default value: `x509`
+  Changing this parameter will create a new cluster resource.
 
 * `authenticating_proxy_ca` - (Optional) CA root certificate provided in the `authenticating_proxy` mode.
   Deprecated, use `authenticating_proxy` instead.

releasenotes/notes/cce-cluster-auth-mode-doc-f8b1ea0b96cbdfe9.yaml

@@ -0,0 +1,4 @@
+---
+other:
+  - |
+    **[CCE]** Update ``authentication_mode`` description in ``resource/opentelekomcloud_cce_cluster_v3`` documentation (`#2788 <https://github.com/opentelekomcloud/terraform-provider-opentelekomcloud/pull/2788>`_)