ESQL: expose transport action to improve usage (#106463)

This commits exposes the query transport action to improve usage. While one can perform all operations prior to this change, it has been suggested that adding the action would improve the symmetry of the API by allowing e.g.

client().execute(builder.action(), builder.request()).actionGet(30, SECONDS);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/esql/action/EsqlQueryRequestBuilder.java

@@ -16,6 +16,8 @@
 public abstract class EsqlQueryRequestBuilder<Request extends EsqlQueryRequest, Response extends EsqlQueryResponse> extends
     ActionRequestBuilder<Request, Response> {
 
+    private final ActionType<Response> action;
+
     /** Creates a new ES|QL query request builder. */
     public static EsqlQueryRequestBuilder<? extends EsqlQueryRequest, ? extends EsqlQueryResponse> newRequestBuilder(
         ElasticsearchClient client
@@ -26,6 +28,11 @@ public abstract class EsqlQueryRequestBuilder<Request extends EsqlQueryRequest,
     // not for direct use
     protected EsqlQueryRequestBuilder(ElasticsearchClient client, ActionType<Response> action, Request request) {
         super(client, action, request);
+        this.action = action;
+    }
+
+    public final ActionType<Response> action() {
+        return action;
     }
 
     public abstract EsqlQueryRequestBuilder<Request, Response> query(String query);

x-pack/plugin/esql/qa/action/src/internalClusterTest/java/org/elasticsearch/test/esql/qa/action/CoreEsqlActionIT.java

@@ -129,8 +129,11 @@ public void testAccessAfterClose() {
 
     protected EsqlQueryResponse run(EsqlQueryRequestBuilder<? extends EsqlQueryRequest, ? extends EsqlQueryResponse> request) {
         try {
+            // The variants here ensure API usage patterns
             if (randomBoolean()) {
                 return request.execute().actionGet(30, SECONDS);
+            } else if (randomBoolean()) {
+                return client().execute(request.action(), request.request()).actionGet(30, SECONDS);
             } else {
                 return ClientHelper.executeWithHeaders(
                     Map.of("Foo", "bar"),