chore: nifi upgrade errata

Author: razvan

modules/ROOT/pages/release-notes.adoc

@@ -425,6 +425,19 @@ Copy any secrets from the default namespace to that used by the operator, as sho
 
 Please note that Java-based products that use the JMX exporter for Prometheus are now built with version https://github.com/prometheus/jmx_exporter/releases/tag/1.0.1[1.0.1], which has breaking changes relevant for any dashboards displaying JVM metrics.
 
+Apache Nifi
+
+To upgrade from 1.x to the 2.x series, the following config overrides are necessary:
+
+----
+spec:
+  configOverrides:
+    nifi.properties:
+      nifi.flow.configuration.file: /stackable/data/database/flow.json.gz
+----
+
+This is necessary because the 2.x versions do not support the XML format for flow definitions anymore. Support for the JSON format has been addded in version 1.16 and both formats have been maintained up to version 2.0.
+
 == Release 24.3
 
 === New / extended platform features