[Stack Monitoring] Do not add empty include array when retrieving logstash pipelines (#202039)

## Summary

This PR fixes the query that retrieves Logstash pipeline stats and
metrics to be displayed in Stack Monitoring. The problem with the
existing query is that a `terms` aggregation contains an empty
`"include": []` filtering array, but that has the nasty effect of
excluding everything and not returning anything, hence the screen is
empty.

The fix is to only add the `include` array if it's not empty. The PR
also fixes a wrong field name used in a cardinality aggregation:
`logstash.node.stats.logstash.uuid` instead of
`logstash_stats.logstash.uuid`

Closes https://github.com/elastic/kibana/issues/202020

### Checklist

- [X] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.

---------

Co-authored-by: Chris Earle <chris.earle@elastic.co>

x-pack/plugins/monitoring/server/lib/metrics/__snapshots__/metrics.test.js.snap

@@ -5981,7 +5981,7 @@ Object {
     "isNotSupportedInInternalCollection": undefined,
     "label": "Pipeline Node Count",
     "legendFormat": undefined,
-    "mbField": undefined,
+    "mbField": "logstash.node.stats.logstash.uuid",
     "metricAgg": undefined,
     "periodsField": undefined,
     "quotaField": undefined,
@@ -6437,7 +6437,7 @@ Object {
     "isNotSupportedInInternalCollection": undefined,
     "label": "Pipeline Node Count",
     "legendFormat": undefined,
-    "mbField": undefined,
+    "mbField": "logstash.node.stats.logstash.uuid",
     "metricAgg": undefined,
     "periodsField": undefined,
     "quotaField": undefined,

x-pack/plugins/monitoring/server/lib/metrics/logstash/classes.ts

@@ -7,11 +7,11 @@
 
 /* eslint-disable max-classes-per-file */
 
-import _ from 'lodash';
 import { i18n } from '@kbn/i18n';
-import { ClusterMetric, Metric, MetricOptions } from '../classes';
-import { LARGE_FLOAT } from '../../../../common/formatting';
+import _ from 'lodash';
 import { NORMALIZED_DERIVATIVE_UNIT } from '../../../../common/constants';
+import { LARGE_FLOAT } from '../../../../common/formatting';
+import { ClusterMetric, Metric, MetricOptions } from '../classes';
 
 const msTimeUnitLabel = i18n.translate('xpack.monitoring.metrics.logstash.msTimeUnitLabel', {
   defaultMessage: 'ms',
@@ -411,7 +411,7 @@ export class LogstashPipelineThroughputMetric extends LogstashMetric {
 
 type LogstashPipelineNodeCountMetricOptions = Pick<
   MetricOptions,
-  'field' | 'label' | 'description' | 'format' | 'units'
+  'field' | 'label' | 'mbField' | 'description' | 'format' | 'units'
 > &
   Partial<Pick<MetricOptions, 'uuidField'>>;
 
@@ -427,15 +427,10 @@ export class LogstashPipelineNodeCountMetric extends LogstashMetric {
     }: {
       pageOfPipelines: Array<{ id: string }>;
     }) => {
-      const termAggExtras: {
-        include: string[];
-      } = {
-        include: [],
-      };
+      const include: string[] | undefined = pageOfPipelines?.length
+        ? pageOfPipelines.map((pipeline) => pipeline.id)
+        : undefined;
 
-      if (pageOfPipelines) {
-        termAggExtras.include = pageOfPipelines.map((pipeline) => pipeline.id);
-      }
       return {
         pipelines_nested: {
           nested: {
@@ -446,7 +441,7 @@ export class LogstashPipelineNodeCountMetric extends LogstashMetric {
               terms: {
                 field: 'logstash_stats.pipelines.id',
                 size: 1000,
-                ...termAggExtras,
+                include,
               },
               aggs: {
                 to_root: {
@@ -472,7 +467,7 @@ export class LogstashPipelineNodeCountMetric extends LogstashMetric {
               terms: {
                 field: 'logstash.node.stats.pipelines.id',
                 size: 1000,
-                ...termAggExtras,
+                include,
               },
               aggs: {
                 to_root: {
@@ -480,7 +475,7 @@ export class LogstashPipelineNodeCountMetric extends LogstashMetric {
                   aggs: {
                     node_count: {
                       cardinality: {
-                        field: this.field,
+                        field: this.mbField,
                       },
                     },
                   },

x-pack/plugins/monitoring/server/lib/metrics/logstash/metrics.ts

@@ -6,23 +6,23 @@
  */
 
 import { i18n } from '@kbn/i18n';
+import {
+  LARGE_ABBREVIATED,
+  LARGE_BYTES,
+  LARGE_FLOAT,
+  SMALL_BYTES,
+} from '../../../../common/formatting';
 import { QuotaMetric } from '../classes';
 import {
-  LogstashEventsRateClusterMetric,
   LogstashEventsLatencyClusterMetric,
-  LogstashEventsRateMetric,
   LogstashEventsLatencyMetric,
+  LogstashEventsRateClusterMetric,
+  LogstashEventsRateMetric,
   LogstashMetric,
+  LogstashPipelineNodeCountMetric,
   LogstashPipelineQueueSizeMetric,
   LogstashPipelineThroughputMetric,
-  LogstashPipelineNodeCountMetric,
 } from './classes';
-import {
-  LARGE_FLOAT,
-  LARGE_BYTES,
-  SMALL_BYTES,
-  LARGE_ABBREVIATED,
-} from '../../../../common/formatting';
 
 const instanceSystemLoadTitle = i18n.translate(
   'xpack.monitoring.metrics.logstash.systemLoadTitle',
@@ -451,6 +451,7 @@ export const metrics = {
   logstash_cluster_pipeline_nodes_count: new LogstashPipelineNodeCountMetric({
     field: 'logstash_stats.logstash.uuid',
     label: pipelineNodeCountLabel,
+    mbField: 'logstash.node.stats.logstash.uuid',
     description: pipelineNodeCountDescription,
     format: LARGE_FLOAT,
     units: '',
@@ -459,6 +460,7 @@ export const metrics = {
     uuidField: 'logstash_stats.logstash.uuid', // TODO: add comment explaining why
     field: 'logstash_stats.logstash.uuid',
     label: pipelineNodeCountLabel,
+    mbField: 'logstash.node.stats.logstash.uuid',
     description: pipelineNodeCountDescription,
     format: LARGE_FLOAT,
     units: '',