ISIS-2794: adds minor doc relating to flushing config property

(cherry picked from commit 118b815)

core/config/src/main/adoc/modules/config/pages/sections/isis.core.runtime-services.adoc

@@ -158,7 +158,7 @@ disable-auto-flush
 
 This key allows this behaviour to be disabled.
 
-Originally introduced as part of ISIS-1134 (fixing memory leaks in the objectstore) where it was found that the autoflush behaviour was causing a (now unrepeatable) data integrity error (see https://issues.apache.org/jira/browse/ISIS-1134?focusedCommentId=14500638&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14500638[ISIS-1134 comment], in the isis-module-security. However, that this could be circumvented by removing the call to flush(). We don't want to break existing apps that might rely on this behaviour, on the other hand we want to fix the memory leak. Adding this configuration property seems the most prudent way forward.
+NOTE: this key is redundant for JPA/EclipseLink, which supports its own auto-flush using https://www.eclipse.org/eclipselink/documentation/2.7/jpa/extensions/persistenceproperties_ref.htm#BABDHEEB[eclipselink.persistence-context.flush-mode]
 
 
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