Similarly to https://github.com/elastic/elasticsearch/pull/97873 but for request handlers: let's stop passing around strings and looking these things up by name on each request when we could just pass around the `Executor` itself.
server/src/main/java/org/elasticsearch/action/support/HandledTransportAction.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.action.support;
import org.elasticsearch.action.ActionRequest;
import org.elasticsearch.action.ActionResponse;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.util.concurrent.EsExecutors;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.transport.TransportChannel;
import org.elasticsearch.transport.TransportRequestHandler;
import org.elasticsearch.transport.TransportService;
import java.util.concurrent.Executor;
/**
 * A TransportAction that self registers a handler into the transport service
 */
public abstract class HandledTransportAction<Request extends ActionRequest, Response extends ActionResponse> extends TransportAction<