docs: remove product-config CLI parameter

Drops the defunct --product-config section from the commandline reference
and notes the removal of product-config validation in the changelog.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: adwk67

CHANGELOG.md

@@ -23,6 +23,7 @@
   The results backend `spec.celeryExecutors.resultBackend` is now `spec.clusterConfig.celeryResultsBackend`.
   The broker `spec.celeryExecutors.broker` is now `spec.clusterConfig.celeryBroker`.
 - Internal operator refactoring: introduce dereference() and validate() steps in the reconciler ([#795]).
+- Removed the product-config based configuration validation. Config and environment overrides are now merged directly from the CRD, and the dereferenced objects are carried on the validated cluster. The `--product-config` CLI flag is now a no-op ([#XXX]).
 - test: Bump vector-aggregator to 0.55.0, replace /graphql call with gRPC call ([#801]).
 
 ### Fixed

docs/modules/airflow/pages/reference/commandline-parameters.adoc

@@ -2,19 +2,6 @@
 
 This operator accepts the following command line parameters:
 
-== product-config
-
-*Default value*: `/etc/stackable/airflow-operator/config-spec/properties.yaml`
-
-*Required*: false
-
-*Multiple values:* false
-
-[source]
-----
-stackable-airflow-operator run --product-config /foo/bar/properties.yaml
-----
-
 == watch-namespace
 
 *Default value*: All namespaces