Add details about info shared, via proxy, with the EPR (#874) (#886)

(cherry picked from commit 0f1c3e6)

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

docs/en/ingest-management/fleet-agent-proxy-package-registry.asciidoc

@@ -17,3 +17,6 @@ example:
 xpack.fleet.registryProxyUrl: your-nat-gateway.corp.net
 ----
 
+== What information is sent to the {package-registry}?
+
+In production environments, {kib}, through the {fleet} plugin, is the only service interacting with the {package-registry}. Communication happens when interacting with the Integrations UI, and when upgrading {kib}. The shared information is about discovery of Elastic packages and their available versions. In general, the only deployment-specific data that is shared is the {kib} version.