Add information about elastic agent diagnostics flow (#789)

* Add information about diagnostics flow

* Update troubleshooting.asciidoc

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>

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Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>
(cherry picked from commit 858e99f)

docs/en/ingest-management/troubleshooting/troubleshooting.asciidoc

@@ -329,7 +329,7 @@ elastic-agent diagnostics
 **Get the diagnostics bundle through {fleet}**
 
 {fleet} provides the ability to remotely generate and gather an {agent}'s diagnostics bundle.
-An agent can gather and upload diagnostics if it is online in a `Healthy` or `Unhealthy` state.
+An agent can gather and upload diagnostics if it is online in a `Healthy` or `Unhealthy` state. The diagnostics are sent to {fleet-server} which in turn adds it into {es}. Therefore, this works even with {agents} that are not using the {es} output.
 To download the diagnostics bundle for local viewing:
 
 . In {kib}, go to **Management -> {fleet} -> Agents**.