Update agent-policies.asciidoc (#1527) (#1624)

* 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 <41695641+kilfoyle@users.noreply.github.com>

---------

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>
(cherry picked from commit 930b490)

Co-authored-by: Insuk (Chris) Cho <isi.cho@gmail.com>

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.
 
 
 [discrete]