Change "module" to "mode" in authorization docs (#15548)

The content describing authorization modes used the term "authorization
modules" erroneously. This patch uses the term "mode" as is appropriate
but keeps the section link header the old "authorization-modules" in
order not to break older links.

content/en/docs/reference/access-authn-authz/authorization.md

@@ -74,8 +74,11 @@ Kubernetes sometimes checks authorization for additional permissions using speci
 of the `bind` verb on `roles` and `clusterroles` resources in the `rbac.authorization.k8s.io` API group.
 * [Authentication](/docs/reference/access-authn-authz/authentication/) layer checks for authorization of the `impersonate` verb on `users`, `groups`, and `serviceaccounts` in the core API group, and the `userextras` in the `authentication.k8s.io` API group.
 
-## Authorization Modules
- * **Node** - A special-purpose authorizer that grants permissions to kubelets based on the pods they are scheduled to run. To learn more about using the Node authorization mode, see [Node Authorization](/docs/reference/access-authn-authz/node/).
+## Authorization Modes {#authorization-modules}
+
+The Kubernetes API server may authorize a request using one of several authorization modes:
+
+ * **Node** - A special-purpose authorization mode that grants permissions to kubelets based on the pods they are scheduled to run. To learn more about using the Node authorization mode, see [Node Authorization](/docs/reference/access-authn-authz/node/).
  * **ABAC** - Attribute-based access control (ABAC) defines an access control paradigm whereby access rights are granted to users through the use of policies which combine attributes together. The policies can use any type of attributes (user attributes, resource attributes, object, environment attributes, etc). To learn more about using the ABAC mode, see [ABAC Mode](/docs/reference/access-authn-authz/abac/).
  * **RBAC** - Role-based access control (RBAC) is a method of regulating access to computer or network resources based on the roles of individual users within an enterprise. In this context, access is the ability of an individual user to perform a specific task, such as view, create, or modify a file. To learn more about using the RBAC mode, see [RBAC Mode](/docs/reference/access-authn-authz/rbac/)
    * When specified RBAC (Role-Based Access Control) uses the `rbac.authorization.k8s.io` API group to drive authorization decisions, allowing admins to dynamically configure permission policies through the Kubernetes API.