docs: Improve upgrade guide

Author: siegfriedweber

docs/modules/opensearch/pages/usage-guide/upgrade.adoc

@@ -3,14 +3,12 @@
 
 == Upgrade from SDP 26.3 to 26.7
 
-=== Hot-reloading of security settings
+=== Dedicated ConfigMap for security settings
 
 The security settings defined in the cluster specification are now stored in a separate ConfigMap named `<cluster-name>-security-config`.
 If you used this name for your custom security configuration, then you must rename it.
 Otherwise the operator will override it.
 
-The operator now supports hot-reloading of security settings.
-
 == Upgrade from SDP 25.11 to 26.3
 
 When upgrading the OpenSearch operator from SDP 25.11 to 26.3, you may encounter several warnings and errors in the operator logs.