Update agent-policies.asciidoc (elastic#1527)

* Update agent-policies.asciidoc

Defend Integration ignores the Custom Fields added in Agent Policy UI as it uses the advanced settings below in the Elastic Defend Integration configuration:
- `windows.advanced.document_enrichment.fields`
- `mac.advanced.document_enrichment.fields`
- `linux.advanced.document_enrichment.fields`

* Update docs/en/ingest-management/agent-policies.asciidoc

Accepting the suggestions! Thanks!

Co-authored-by: David Kilfoyle <[email protected]>

---------

Co-authored-by: David Kilfoyle <[email protected]>

Author: insukcho

docs/en/ingest-management/agent-policies.asciidoc

@@ -305,6 +305,7 @@ Note that adding custom tags is not supported for a small set of inputs:
 * `cloud-defend`
 * `fleet-server`
 * `pf-elastic-collector`, `pf-elastic-symbolizer`, and `pf-host-agent`
+* `endpoint` inputs. Instead, use the advanced settings (`*.advanced.document_enrichment.fields`) of the {elastic-defend} Integration.
 
 
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