Force execution of fetch tasks (#31974)

Forces fetch tasks to queue even in the event that the queue is
already full. The reasoning is that fetch tasks may only be follow-up
to query tasks, so the number of additional fetch tasks that may enter
the threadpool is expected to be reasonable.

Closes #29442

Author: imotov

server/src/main/java/org/elasticsearch/action/search/SearchTransportService.java

@@ -432,7 +432,7 @@ public void messageReceived(ShardFetchRequest request, TransportChannel channel,
             });
         TransportActionProxy.registerProxyAction(transportService, FETCH_ID_SCROLL_ACTION_NAME, FetchSearchResult::new);
 
-        transportService.registerRequestHandler(FETCH_ID_ACTION_NAME, ShardFetchSearchRequest::new, ThreadPool.Names.SEARCH,
+        transportService.registerRequestHandler(FETCH_ID_ACTION_NAME, ShardFetchSearchRequest::new, ThreadPool.Names.SEARCH, true, true,
             new TaskAwareTransportRequestHandler<ShardFetchSearchRequest>() {
                 @Override
                 public void messageReceived(ShardFetchSearchRequest request, TransportChannel channel, Task task) throws Exception {