Add elasticsearch_client stats to the monitoring index templates. (#91508)

* Add elasticsearch_client stats to monitoring-kibana MB index template

* Add PR to changelog

* Store only most interesting stats

* Update x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/monitoring/exporter/MonitoringTemplateUtils.java

Co-authored-by: Carlos Crespo <crespocarlos@users.noreply.github.com>

* Update x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/MonitoringTemplateRegistry.java

Co-authored-by: Carlos Crespo <crespocarlos@users.noreply.github.com>

Co-authored-by: Carlos Crespo <crespocarlos@users.noreply.github.com>

docs/changelog/91508.yaml

@@ -0,0 +1,5 @@
+pr: 91508
+summary: "Add kibana.stats.elasticsearch_client stats to the monitoring index templates."
+area: Monitoring
+type: enhancement
+issues: []

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/monitoring/exporter/MonitoringTemplateUtils.java

@@ -19,7 +19,7 @@ public final class MonitoringTemplateUtils {
      * <p>
      * It may be possible for this to diverge between templates and pipelines, but for now they're the same.
      */
-    public static final int LAST_UPDATED_VERSION = Version.V_8_1_0.id;
+    public static final int LAST_UPDATED_VERSION = Version.V_8_7_0.id;
 
     /**
      * Current version of templates used in their name to differentiate from breaking changes (separate from product version).

x-pack/plugin/core/src/main/resources/monitoring-kibana-mb.json

@@ -219,6 +219,19 @@
                     }
                   }
                 },
+                "elasticsearch_client": {
+                  "properties": {
+                    "total_active_sockets": {
+                      "type": "integer"
+                    },
+                    "total_idle_sockets": {
+                      "type": "integer"
+                    },
+                    "total_queued_requests": {
+                      "type": "integer"
+                    }
+                  }
+                },
                 "kibana": {
                   "properties": {
                     "status": {

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/MonitoringTemplateRegistry.java

@@ -50,7 +50,7 @@ public class MonitoringTemplateRegistry extends IndexTemplateRegistry {
      * continue to use the release version number in this registry, even though this is not standard practice for template
      * registries.
      */
-    public static final int REGISTRY_VERSION = Version.V_8_1_0.id;
+    public static final int REGISTRY_VERSION = Version.V_8_7_0.id;
     private static final String REGISTRY_VERSION_VARIABLE = "xpack.monitoring.template.release.version";
 
     /**