[DOCS] Update Fleet Server guide - Fleet Server keeps using the ES ho…

…st provided at install/enroll time. (#1185) (#1191)

* [DOCS] Update Fleet Server guide

* Update docs/en/ingest-management/fleet/add-fleet-server-on-prem.asciidoc

* Update docs/en/ingest-management/fleet/add-fleet-server-on-prem.asciidoc

Co-authored-by: Karen Metts <35154725+karenzone@users.noreply.github.com>

---------

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>
Co-authored-by: Karen Metts <35154725+karenzone@users.noreply.github.com>
(cherry picked from commit 7257560)

Co-authored-by: Luca Belluccini <luca.belluccini@elastic.co>

docs/en/ingest-management/fleet/add-fleet-server-on-prem.asciidoc

@@ -213,6 +213,9 @@ token for each {fleet-server}. For other ways to generate service tokens, refer
 `--fleet-server-port` options in the `elastic-agent install` command. Refer to the 
 {fleet-guide}/elastic-agent-cmd-options.html#elastic-agent-install-command[install command documentation]
 for details.
+* Please note that {fleet-server} will keep using the {es} host provided via `--fleet-server-host` at install time. 
+The {es} hosts configured in the associated policy will be ignored by the {fleet-server} integration. 
+We strongly recommend using a load balancer to avoid coupling the {fleet-server} to the provided host.
 ====
 +
 At the *Install Fleet Server to a centralized host* step,