[Monitoring] Add cluster metadata to cluster_stats docs (#33860)

* WIP

* Adding cluster metadata to cluster stats monitoring doc

* Fixing checkstyle errors

* Adding missing license header

* Updating tests

* Getting cluster settings from cluster state

* Removing more unnecessary changes

* Adding cluster metadata settings to cluster_stats docs

* Updating test to include cluster metadata

* Fixing checkstyle

* Guarding against NPE

* Updating test fixture

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsCollector.java

@@ -112,7 +112,8 @@ public class ClusterStatsCollector extends Collector {
         // Adds a cluster stats document
         return Collections.singleton(
                 new ClusterStatsMonitoringDoc(clusterUuid, timestamp(), interval, node, clusterName, version,  clusterStats.getStatus(),
-                                              license, apmIndicesExist, xpackUsage, clusterStats, clusterState, clusterNeedsTLSEnabled));
+                                              license, apmIndicesExist, xpackUsage, clusterStats, clusterState,
+                                              clusterNeedsTLSEnabled));
     }
 
     boolean doAPMIndicesExist(final ClusterState clusterState) {

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDoc.java

@@ -8,10 +8,12 @@ package org.elasticsearch.xpack.monitoring.collector.cluster;
 import org.elasticsearch.action.admin.cluster.stats.ClusterStatsResponse;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.health.ClusterHealthStatus;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.collect.MapBuilder;
+import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.license.License;
@@ -45,6 +47,7 @@ public class ClusterStatsMonitoringDoc extends MonitoringDoc {
                                 ClusterState.Metric.NODES));
 
     public static final String TYPE = "cluster_stats";
+    protected static final String SETTING_CLUSTER_METADATA = "cluster.metadata";
 
     private final String clusterName;
     private final String version;
@@ -118,6 +121,14 @@ public class ClusterStatsMonitoringDoc extends MonitoringDoc {
         return clusterNeedsTLSEnabled;
     }
 
+    Settings getClusterMetaDataSettings() {
+        MetaData metaData = this.clusterState.getMetaData();
+        if (metaData == null) {
+            return Settings.EMPTY;
+        }
+        return metaData.settings().getAsSettings(SETTING_CLUSTER_METADATA);
+    }
+
     @Override
     protected void innerToXContent(XContentBuilder builder, Params params) throws IOException {
         builder.field("cluster_name", clusterName);
@@ -156,6 +167,25 @@ public class ClusterStatsMonitoringDoc extends MonitoringDoc {
             builder.endObject();
         }
 
+        Settings clusterMetaDataSettings = getClusterMetaDataSettings();
+        if (clusterMetaDataSettings != null) {
+            builder.startObject("cluster_settings");
+            {
+                if (clusterMetaDataSettings.size() > 0) {
+                    builder.startObject("cluster");
+                    {
+                        builder.startObject("metadata");
+                        {
+                            clusterMetaDataSettings.toXContent(builder, params);
+                        }
+                        builder.endObject();
+                    }
+                    builder.endObject();
+                }
+            }
+            builder.endObject();
+        }
+
         builder.startObject("stack_stats");
         {
             // in the future, it may be useful to pass in an object that represents APM (and others), but for now this

x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java

@@ -203,7 +203,12 @@ public class ClusterStatsMonitoringDocTests extends BaseMonitoringDocTestCase<Cl
                                                                 Version.V_6_0_0_beta1);
 
         final ClusterState clusterState = ClusterState.builder(clusterName)
-                                                        .metaData(MetaData.builder().clusterUUID(clusterUuid).build())
+                                                        .metaData(MetaData.builder()
+                                                            .clusterUUID(clusterUuid)
+                                                            .transientSettings(Settings.builder()
+                                                                .put("cluster.metadata.display_name", "my_prod_cluster")
+                                                                .build())
+                                                            .build())
                                                         .stateUUID("_state_uuid")
                                                         .version(12L)
                                                         .nodes(DiscoveryNodes.builder()
@@ -521,6 +526,13 @@ public class ClusterStatsMonitoringDocTests extends BaseMonitoringDocTestCase<Cl
                       + "}"
                     + "}"
                   + "},"
+                  + "\"cluster_settings\":{"
+                    + "\"cluster\":{"
+                      + "\"metadata\":{"
+                        + "\"display_name\":\"my_prod_cluster\""
+                      + "}"
+                    + "}"
+                  + "},"
                   + "\"stack_stats\":{"
                     + "\"apm\":{"
                       + "\"found\":" + apmIndicesExist