Enable Fleet UI for serverless search projects (elastic#195774)

## Summary

Enable Fleet UI for serverless search projects. This is needed to enable
upcoming agentless features.

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

---------

Co-authored-by: Julien Lind <julien.lind@elastic.co>

config/serverless.es.yml

@@ -10,10 +10,42 @@ xpack.observability.enabled: false
 xpack.securitySolution.enabled: false
 xpack.serverless.observability.enabled: false
 enterpriseSearch.enabled: false
-xpack.fleet.enabled: false
 xpack.observabilityAIAssistant.enabled: false
 xpack.osquery.enabled: false
 
+# Enable fleet on search projects for agentless features
+xpack.fleet.enabled: true
+xpack.fleet.internal.registry.kibanaVersionCheckEnabled: false
+xpack.fleet.internal.registry.spec.min: '3.0'
+xpack.fleet.internal.registry.spec.max: '3.2'
+xpack.fleet.packages:
+  # fleet_server package installed to publish agent metrics
+  - name: fleet_server
+    version: latest
+# Filter out some observability and security integrations
+xpack.fleet.internal.registry.excludePackages: [
+  # Security integrations
+  'endpoint',
+  'beaconing',
+  'cloud_security_posture',
+  'cloud_defend',
+  'security_detection_engine',
+
+  # Oblt integrations
+  'apm',
+  'synthetics',
+  'synthetics_dashboards',
+
+  # Removed in 8.11 integrations
+  'cisco',
+  'microsoft',
+  'symantec',
+  'cyberark',
+
+  # Profiling integrations
+  'profiler_agent',
+]
+
 ## Fine-tune the search solution feature privileges. Also, refer to `serverless.yml` for the project-agnostic overrides.
 xpack.features.overrides:
   ### Dashboards feature is moved from Analytics category to the Search one.