Need to add "raw" as a node/container level request writer (#4123)

This follows up PR#4073 to complete the migration.

Author: epugh

solr/core/src/java/org/apache/solr/response/ResponseWritersRegistry.java

@@ -55,6 +55,8 @@ private ResponseWritersRegistry() {
             jsonWriter, // Alias for JSON
             "xml",
             new XMLResponseWriter(),
+            "raw",
+            new RawResponseWriter(),
             PROMETHEUS_METRICS_WT,
             prometheusWriter,
             OPEN_METRICS_WT,

solr/core/src/test/org/apache/solr/handler/admin/ZookeeperInfoHandlerTest.java

@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.handler.admin;
+
+import java.io.IOException;
+import org.apache.solr.client.solrj.SolrClient;
+import org.apache.solr.client.solrj.SolrRequest;
+import org.apache.solr.client.solrj.SolrServerException;
+import org.apache.solr.client.solrj.request.CollectionAdminRequest;
+import org.apache.solr.client.solrj.request.GenericSolrRequest;
+import org.apache.solr.client.solrj.response.SimpleSolrResponse;
+import org.apache.solr.client.solrj.response.json.JsonMapResponseParser;
+import org.apache.solr.cloud.SolrCloudTestCase;
+import org.apache.solr.common.params.CommonParams;
+import org.apache.solr.common.params.ModifiableSolrParams;
+import org.apache.solr.common.util.NamedList;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+/** Basic tests for {@link ZookeeperInfoHandler} */
+public class ZookeeperInfoHandlerTest extends SolrCloudTestCase {
+
+  @BeforeClass
+  public static void setupCluster() throws Exception {
+    configureCluster(1).addConfig("conf", configset("cloud-minimal")).configure();
+  }
+
+  @Test
+  public void testZkInfoHandler() throws SolrServerException, IOException {
+    SolrClient client = cluster.getSolrClient();
+
+    ModifiableSolrParams params = new ModifiableSolrParams();
+    params.set(CommonParams.PATH, "/");
+    params.set("detail", "true");
+    GenericSolrRequest req =
+        new GenericSolrRequest(SolrRequest.METHOD.GET, "/admin/zookeeper", params);
+    req.setResponseParser(new JsonMapResponseParser());
+
+    NamedList<Object> response = client.request(req);
+    assertNotNull("Response should not be null", response);
+
+    // ZK handler should return 'znode' for detail requests
+    assertNotNull(response.get("znode"));
+  }
+
+  @Test
+  public void testZkInfoHandlerCollectionsView() throws Exception {
+    // Create a test collection first
+    String collectionName = "zkinfo_test_collection";
+    CollectionAdminRequest.createCollection(collectionName, "conf", 1, 1)
+        .process(cluster.getSolrClient());
+    cluster.waitForActiveCollection(collectionName, 1, 1);
+
+    SolrClient client = cluster.getSolrClient();
+    // Test collections view (graph view with clusterstate.json)
+    ModifiableSolrParams params = new ModifiableSolrParams();
+    params.set(CommonParams.PATH, "/clusterstate.json");
+    params.set("view", "graph");
+
+    GenericSolrRequest req =
+        new GenericSolrRequest(SolrRequest.METHOD.GET, "/admin/zookeeper", params);
+    req.setResponseParser(new JsonMapResponseParser());
+
+    // Verify the request completes and returns collection data
+    SimpleSolrResponse response = req.process(client);
+    NamedList<Object> responseData = response.getResponse();
+
+    // Collections view should return znode with collection data
+    assertNotNull("Response should not be null", responseData);
+
+    assertNotNull(
+        "Response should contain 'znode' for collections view", responseData.get("znode"));
+  }
+}