[Inventory v2] Fix issue with logs only views (#207305)

Closes https://github.com/elastic/kibana/issues/206967

## Summary

After some changes related to V2 migration of getting the entities,
there was an issue with the new data coming from the endpoint - the
`data_stream.type` is a string instead of an array in case of a single
data stream so this PR adds a fix to support that (and a test)

## Bug fixes
- Service overview page loads for a logs-only data stream
- After adding the fix, I saw another error related to the `useTheme`
and changed it to use the `euiTheme` similar to the other changes
related to the Borealis team upgrade

## Testing
To test the scenario with services and hosts coming from logs (without
APM / metrics) I added a new scenario in synthtrace so to test then we
should:
- Run the new scenario: `node scripts/synthtrace logs_only` (if possible
on a clean ES)
- Enable `observability:entityCentricExperience` in Stack Management >
Advanced Setting
- Go to Inventory and click on a service
   - The logs-only views should be available
- Go to Inventory and click on a host
   - The logs-only views should be available
   


https://github.com/user-attachments/assets/cfd5fd40-ac44-4807-9a29-f3ee3015d814


 - Test one of the scenarios with mix of APM/metrics/logs
    - Run `node scripts/synthtrace infra_hosts_with_apm_hosts`
- Enable `observability:entityCentricExperience` in Stack Management >
Advanced Setting
    - Go to Inventory and click on a service from APM
       - The APM views (service/traces) should be available
    - Go to Inventory and click on a host
       - The asset details view should be available and show metrics
     


https://github.com/user-attachments/assets/894c7c1a-aaa1-42cb-9dcb-05c9a5ca8177



- Infrastructure (Inventory/Hosts, etc) and Applications (Service
Inventory/Traces, etc) should load the data for this scenario and not
for the logs only (also for an oblt cluster connection)
    
    


https://github.com/user-attachments/assets/4d092cc6-a8ad-4022-b980-b443be09acc9

packages/kbn-apm-synthtrace/src/scenarios/logs_only.ts

@@ -0,0 +1,79 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { LogDocument, log, generateShortId, generateLongId } from '@kbn/apm-synthtrace-client';
+import { Scenario } from '../cli/scenario';
+import { withClient } from '../lib/utils/with_client';
+import { parseLogsScenarioOpts } from './helpers/logs_scenario_opts_parser';
+import { IndexTemplateName } from '../lib/logs/custom_logsdb_index_templates';
+import { getCluster, getCloudRegion, getCloudProvider } from './helpers/logs_mock_data';
+
+const MESSAGE_LOG_LEVELS = [
+  { message: 'A simple log', level: 'info' },
+  { message: 'Yet another debug log', level: 'debug' },
+  { message: 'Error with certificate: "ca_trusted_fingerprint"', level: 'error' },
+];
+
+const scenario: Scenario<LogDocument> = async (runOptions) => {
+  const { isLogsDb } = parseLogsScenarioOpts(runOptions.scenarioOpts);
+
+  return {
+    bootstrap: async ({ logsEsClient }) => {
+      if (isLogsDb) await logsEsClient.createIndexTemplate(IndexTemplateName.LogsDb);
+    },
+    generate: ({ range, clients: { logsEsClient } }) => {
+      const { logger } = runOptions;
+
+      const SERVICE_NAMES = Array(3)
+        .fill(null)
+        .map((_, idx) => `synth-service-logs-${idx}`);
+
+      const logs = range
+        .interval('1m')
+        .rate(1)
+        .generator((timestamp) => {
+          return Array(20)
+            .fill(0)
+            .map(() => {
+              const index = Math.floor(Math.random() * 3);
+              const { clusterId, clusterName } = getCluster(index);
+              const cloudRegion = getCloudRegion(index);
+              return log
+                .create({ isLogsDb })
+                .message(MESSAGE_LOG_LEVELS[index].message)
+                .logLevel(MESSAGE_LOG_LEVELS[index].level)
+                .service(SERVICE_NAMES[index])
+                .defaults({
+                  'trace.id': generateShortId(),
+                  'agent.name': 'synth-agent',
+                  'orchestrator.cluster.name': clusterName,
+                  'orchestrator.cluster.id': clusterId,
+                  'orchestrator.resource.id': generateShortId(),
+                  'cloud.provider': getCloudProvider(),
+                  'cloud.region': cloudRegion,
+                  'cloud.availability_zone': `${cloudRegion}a`,
+                  'cloud.project.id': generateShortId(),
+                  'cloud.instance.id': generateShortId(),
+                  'log.file.path': `/logs/${generateLongId()}/error.txt`,
+                })
+                .timestamp(timestamp);
+            });
+        });
+
+      return [
+        withClient(
+          logsEsClient,
+          logger.perf('generating_logs', () => logs)
+        ),
+      ];
+    },
+  };
+};
+
+export default scenario;

x-pack/solutions/observability/plugins/apm/server/routes/entities/utils/merge_entities.test.ts

@@ -302,4 +302,27 @@ describe('mergeEntities', () => {
       },
     ]);
   });
+  it('has a single data stream type and no environment', () => {
+    const entities: EntityLatestServiceRaw[] = [
+      {
+        'data_stream.type': 'logs',
+        'agent.name': ['nodejs', 'nodejs'],
+        'entity.last_seen_timestamp': '2024-12-13T14:52:35.461Z',
+        'service.name': 'service-1',
+        'entity.type': 'built_in_services_from_ecs_data',
+        'entity.id': 'service-1:test',
+        'entity.display_name': 'service-1',
+      },
+    ];
+    const result = mergeEntities({ entities });
+    expect(result).toEqual([
+      {
+        agentName: 'nodejs' as AgentName,
+        dataStreamTypes: ['logs'],
+        environments: [],
+        lastSeenTimestamp: '2024-12-13T14:52:35.461Z',
+        serviceName: 'service-1',
+      },
+    ]);
+  });
 });

x-pack/solutions/observability/plugins/apm/server/routes/entities/utils/merge_entities.ts

@@ -5,7 +5,7 @@
  * 2.0.
  */
 
-import { compact, uniq } from 'lodash';
+import { castArray, compact, uniq } from 'lodash';
 import type { EntityDataStreamType } from '@kbn/observability-shared-plugin/common';
 import type { EntityLatestServiceRaw } from '../types';
 import type { AgentName } from '../../../../typings/es_schemas/ui/fields/agent';
@@ -49,7 +49,7 @@ function mergeFunc(entity: EntityLatestServiceRaw, existingEntity?: MergedServic
   if (!existingEntity) {
     return {
       ...commonEntityFields,
-      dataStreamTypes: uniq(entity['data_stream.type']),
+      dataStreamTypes: uniq(castArray(entity['data_stream.type'])),
       environments: uniq(
         compact(
           Array.isArray(entity['service.environment'])
@@ -62,7 +62,10 @@ function mergeFunc(entity: EntityLatestServiceRaw, existingEntity?: MergedServic
   return {
     ...commonEntityFields,
     dataStreamTypes: uniq(
-      compact([...(existingEntity?.dataStreamTypes ?? []), ...entity['data_stream.type']])
+      compact([
+        ...(existingEntity?.dataStreamTypes ?? []),
+        ...castArray(entity['data_stream.type']),
+      ])
     ),
     environments: uniq(compact([...existingEntity?.environments, entity['service.environment']])),
   };

x-pack/solutions/observability/plugins/observability_shared/public/components/add_data_panel/index.tsx

@@ -8,6 +8,7 @@
 /* eslint-disable @elastic/eui/href-or-on-click */
 
 import {
+  COLOR_MODES_STANDARD,
   EuiButton,
   EuiButtonIcon,
   EuiFlexGroup,
@@ -22,7 +23,6 @@ import {
 } from '@elastic/eui';
 import React from 'react';
 import { i18n } from '@kbn/i18n';
-import { useTheme } from '../../hooks/use_theme';
 
 interface AddDataPanelContent {
   title: string;
@@ -78,11 +78,10 @@ export function AddDataPanel({
   onAddData,
   'data-test-subj': dataTestSubj,
 }: AddDataPanelProps) {
-  const { euiTheme } = useEuiTheme();
-  const theme = useTheme();
-  const imgSrc = `${content.img?.baseFolderPath}/${theme.darkMode ? 'dark' : 'light'}/${
-    content.img?.name
-  }`;
+  const { euiTheme, colorMode } = useEuiTheme();
+  const imgSrc = `${content.img?.baseFolderPath}/${
+    colorMode === COLOR_MODES_STANDARD.dark ? 'dark' : 'light'
+  }/${content.img?.name}`;
 
   return (
     <>