[Fleet] Add modified_ilms telemetry to fleet_usages (#243637)

## Summary

Relates elastic/ingest-dev#6085

Add `modified_ilms` to `fleet_usages` telemetry to track how many
clusters have these ILM modified by users.

To verify:
- modify one of the ILMs e.g. synthetics
- wait for the fleet usage sender to run (hourly schedule)
- check that `modified_ilms` array has `synthetics` in it

```
[2025-11-20T13:44:01.394+01:00][DEBUG][plugins.fleet] Fleet usage telemetry: {"agents_enabled":true,...,"modified_ilms":["synthetics"]}
```


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] 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.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [ ] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

Author: juliaElastic

x-pack/platform/plugins/shared/fleet/server/collectors/modified_ilms.test.ts

@@ -0,0 +1,27 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { getModifiedILMs } from './modified_ilms';
+
+jest.mock('../services/epm/elasticsearch/template/default_settings', () => {
+  return {
+    getILMPolicies: jest.fn().mockResolvedValue(
+      new Map([
+        ['logs', { deprecatedILMPolicy: { version: 2 }, newILMPolicy: { version: 1 } }],
+        ['metrics', { deprecatedILMPolicy: { version: 1 }, newILMPolicy: { version: 3 } }],
+        ['synthetics', { deprecatedILMPolicy: { version: 2 }, newILMPolicy: { version: 1 } }],
+      ])
+    ),
+  };
+});
+
+describe('getModifiedILMs', () => {
+  it('should return an array of modified ILM policy names', async () => {
+    const modifiedILMs = await getModifiedILMs();
+    expect(modifiedILMs).toEqual(['logs', 'metrics@lifecycle', 'synthetics']);
+  });
+});

x-pack/platform/plugins/shared/fleet/server/collectors/modified_ilms.ts

@@ -0,0 +1,30 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { appContextService } from '../services';
+import { getILMPolicies } from '../services/epm/elasticsearch/template/default_settings';
+
+export async function getModifiedILMs(): Promise<string[]> {
+  const isILMPolicyDisabled = appContextService.getConfig()?.internal?.disableILMPolicies ?? false;
+  if (isILMPolicyDisabled) {
+    return [];
+  }
+  const dataStreamTypes = ['logs', 'metrics', 'synthetics'];
+  const ilmPolicies = await getILMPolicies(dataStreamTypes);
+  const modifiedILMs: string[] = [];
+
+  ilmPolicies.forEach((policies, dataStreamType) => {
+    const { deprecatedILMPolicy, newILMPolicy } = policies;
+    if ((deprecatedILMPolicy?.version ?? 1) > 1) {
+      modifiedILMs.push(dataStreamType);
+    }
+    if ((newILMPolicy?.version ?? 1) > 1) {
+      modifiedILMs.push(`${dataStreamType}@lifecycle`);
+    }
+  });
+  return modifiedILMs;
+}

x-pack/platform/plugins/shared/fleet/server/collectors/register.ts

@@ -28,6 +28,7 @@ import type { AgentsPerOutputType } from './agents_per_output';
 import { getAgentsPerOutput } from './agents_per_output';
 import type { IntegrationsDetails } from './integrations_collector';
 import { getIntegrationsDetails } from './integrations_collector';
+import { getModifiedILMs } from './modified_ilms';
 
 export interface Usage {
   agents_enabled: boolean;
@@ -50,6 +51,7 @@ export interface FleetUsage extends Usage, AgentData {
   fleet_server_logs_top_errors?: string[];
   agents_per_output_type: AgentsPerOutputType[];
   integrations_details: IntegrationsDetails[];
+  modified_ilms: string[];
 }
 
 export const fetchFleetUsage = async (
@@ -77,6 +79,7 @@ export const fetchFleetUsage = async (
     deployment_id: appContextService.getCloud()?.deploymentId,
     integrations_details: await getIntegrationsDetails(soClient),
     agentless_agents: await getAgentUsage(soClient, esClient, true),
+    modified_ilms: await getModifiedILMs(),
   };
   return usage;
 };

x-pack/platform/plugins/shared/fleet/server/services/telemetry/fleet_usages_schema.ts

@@ -517,6 +517,13 @@ export const fleetUsagesSchema: RootSchema<any> = {
     type: 'keyword',
     _meta: { description: 'id of the deployment', optional: true },
   },
+  modified_ilms: {
+    type: 'array',
+    items: {
+      type: 'keyword',
+      _meta: { description: 'list of managed ILMs modified by users' },
+    },
+  },
 };
 
 export const fleetIntegrationsSchema: RootSchema<any> = {