docs(clients): mark apiVersion as @internal (#2019)

* chore(clients): mark apiVersion as internal

* chore: amention API version is set by SDK

* chore: explicitly call out it is not be used by customer code

Author: trivikr

packages/smithy-client/src/client.ts

@@ -3,6 +3,11 @@ import { Client as IClient, Command, MetadataBearer, RequestHandler } from "@aws
 
 export interface SmithyConfiguration<HandlerOptions> {
   requestHandler: RequestHandler<any, any, HandlerOptions>;
+  /**
+   * The API version set internally by the SDK, and is
+   * not planned to be used by customer code.
+   * @internal
+   */
   readonly apiVersion: string;
 }