[Fleet] install custom assets on remote cluster

[juliaElastic]

Summary

Closes #206244

Install custom assets on the remote cluster

To test locally:

• enable feature flag enableSyncIntegrationsOnRemote
• Create ccr index with some custom ingest pipelines and component templates

PUT fleet-synced-integrations-ccr-remote1/_doc/fleet-synced-integrations
{
  "id": "fleet-synced-integrations",
          "remote_es_hosts": [
            {
              "name": "Preconfiged remote output",
              "hosts": [
                "http://192.168.64.1:9200"
              ],
              "sync_integrations": true
            }
          ],
          "integrations": [
            {
              "package_name": "elastic_agent",
              "package_version": "2.2.0",
              "updated_at": "2025-03-24T09:36:12.127Z"
            },
            {
              "package_name": "endpoint",
              "package_version": "9.0.0",
              "updated_at": "2025-03-24T09:35:58.257Z"
            },
            {
              "package_name": "fleet_server",
              "package_version": "1.6.0",
              "updated_at": "2025-03-24T09:29:04.081Z"
            },
            {
              "package_name": "system",
              "package_version": "1.67.3",
              "updated_at": "2025-03-24T09:36:11.981Z"
            }
          ],
          "custom_assets": {
            "component_template:logs-system.auth@custom": {
              "type": "component_template",
              "name": "logs-system.auth@custom",
              "package_name": "system",
              "package_version": "1.67.3",
              "is_deleted": false,
              "template": {
                "mappings": {
                  "properties": {
                    "field1": {
                      "type": "text"
                    }
                  }
                }
              }
            },
            "ingest_pipeline:logs-system.auth@custom": {
              "type": "ingest_pipeline",
              "name": "logs-system.auth@custom",
              "package_name": "system",
              "package_version": "1.67.3",
              "is_deleted": false,
              "pipeline": {
                "processors": [
                  {
                    "set": {
                      "field": "test_field",
                      "value": "value"
                    }
                  }
                ]
              }
            }
          }
        }

• Wait 5m for the sync task to run
• Verify that the custom assets are created

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 5d13c67

Metrics [docs]

✅ unchanged

History

• 💛 Build #286409 was flaky 07b1818
• 💚 Build #286171 succeeded 3e33365

cc @juliaElastic

[nchaulet]

code LGTM 🚀

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)