add notes (#4779)

Author: colleenmcginnis

docs/en/observability/apm/collect-application-data/agents/agent-configuration.asciidoc

@@ -5,6 +5,11 @@
 <titleabbrev>Centrally configure APM agents in Kibana</titleabbrev>
 ++++
 
+[NOTE]
+====
+APM agent central configuration is _not_ compatible with {serverless-docs}[{serverless-full}].
+====
+
 APM Agent configuration allows you to fine-tune your APM agent configuration from within the Applications UI.
 Changes are automatically propagated to your APM agents, so there's no need to redeploy.
 

docs/en/observability/apm/data-model/transactions/sampling.asciidoc

@@ -116,9 +116,12 @@ Refer to the documentation of your favorite OpenTelemetry agent or SDK for more
 == Tail-based sampling
 
 [NOTE]
+.Support for tail-based sampling
 ====
 Tail-based sampling is only supported when writing to {es}.
 If you are using a different <<apm-configuring-output,output>>, tail-based sampling is _not_ supported.
+
+Tail-based sampling is _not_ compatible with {serverless-docs}[{serverless-full}].
 ====
 
 In tail-based sampling, the sampling decision for each trace is made after the trace has completed.

docs/en/observability/apm/security/elastic-stack/feature-roles.asciidoc

@@ -5,6 +5,11 @@
 <titleabbrev>Use feature roles</titleabbrev>
 ++++
 
+[NOTE]
+====
+Kibana custom roles are _not_ compatible with {serverless-docs}[{serverless-full}].
+====
+
 Manage access on a feature-by-feature basis by creating several custom feature-related _roles_ and assigning one or more of these roles to each _user or group_ based on which features they need to access.
 
 [TIP]