[8.x](backport #4281) Add limitations to EEM docs (#4289)

* Add limitations to EEM docs (#4281)

* add eem limitations to serverless docs

* add eem limitations to stateful docs

(cherry picked from commit 86fd7fc)

# Conflicts:
#	docs/en/serverless/elastic-entity-model.mdx

* Delete docs/en/serverless directory

---------

Co-authored-by: Colleen McGinnis <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

docs/en/observability/elastic-entity-model.asciidoc

@@ -65,3 +65,11 @@ The following {es} privileges are required to delete {es} resources:
 |application: `kibana-.kibana`, privileges: [`saved_object:entity-definition/delete`, `saved_object:entity-discovery-api-key/delete`], resources: [*]
 |====
 
+[discrete]
+[[elastic-entity-model-limitations]]
+== Limitations
+
+* {ref}/modules-cross-cluster-search.html[Cross-cluster search (CCS)] is not supported.
+  EEM cannot leverage data stored on a remote cluster.
+* Services are only detected from documents where `service.name` is detected in index
+  patterns that match either `logs-*` or `apm-*`.