Make the search endpoint for search application cancellable (#95539)

This commit ensures that the search is cancelled when the http channel is closed in the middle of a request

Author: jimczi

x-pack/plugin/ent-search/src/main/java/org/elasticsearch/xpack/application/search/action/RestQuerySearchApplicationAction.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.rest.RestRequest;
 import org.elasticsearch.rest.Scope;
 import org.elasticsearch.rest.ServerlessScope;
+import org.elasticsearch.rest.action.RestCancellableNodeClient;
 import org.elasticsearch.rest.action.RestChunkedToXContentListener;
 import org.elasticsearch.xpack.application.EnterpriseSearch;
 
@@ -45,7 +46,9 @@ protected RestChannelConsumer prepareRequest(RestRequest restRequest, NodeClient
         } else {
             request = new SearchApplicationSearchRequest(searchAppName);
         }
-        final SearchApplicationSearchRequest finalRequest = request;
-        return channel -> client.execute(QuerySearchApplicationAction.INSTANCE, finalRequest, new RestChunkedToXContentListener<>(channel));
+        return channel -> {
+            RestCancellableNodeClient cancelClient = new RestCancellableNodeClient(client, restRequest.getHttpChannel());
+            cancelClient.execute(QuerySearchApplicationAction.INSTANCE, request, new RestChunkedToXContentListener<>(channel));
+        };
     }
 }