Adds external link to ack_watch API (#4607)

Author: kosabogi

output/openapi/elasticsearch-openapi.json

@@ -1,3 +1,4 @@
+ack-watch, https://www.elastic.co/docs/explore-analyze/alerts-cases/watcher/actions#example
 apis,https://www.elastic.co/docs/api/doc/elasticsearch
 add-nodes,https://www.elastic.co/docs/deploy-manage/maintenance/add-and-remove-elasticsearch-nodes
 alias-update,https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-put-alias

output/schema/schema.json

@@ -31,10 +31,12 @@ import { Name, Names } from '@_types/common'
  *
  * Acknowledging an action throttles further executions of that action until its `ack.state` is reset to `awaits_successful_execution`.
  * This happens when the condition of the watch is not met (the condition evaluates to false).
+ * To demonstrate how throttling works in practice and how it can be configured for individual actions within a watch, refer to External documentation.
  * @rest_spec_name watcher.ack_watch
  * @availability stack stability=stable
  * @cluster_privileges manage_watcher
  * @doc_id watcher-api-ack-watch
+ * @ext_doc_id ack-watch
  */
 export interface Request extends RequestBase {
   urls: [