docs(iceberg): Add DLQ table retention note to Iceberg data retention section (#1597)

Author: nvartolomei

modules/manage/pages/iceberg/about-iceberg-topics.adoc

@@ -242,6 +242,8 @@ Data in an Iceberg-enabled topic is consumable from Kafka based on the configure
 - Explicitly delete data from the Iceberg table using a query engine.
 - Disable the Iceberg integration for the topic and delete the Parquet files in object storage.
 
+The DLQ table (`<topic-name>~dlq`) follows the same persistence rules as the main Iceberg table.
+
 == Schema evolution
 
 Redpanda supports schema evolution in accordance with the https://iceberg.apache.org/spec/#schema-evolution[Iceberg specification^]. Permitted schema evolutions include reordering fields and promoting field types. When you update the schema in Schema Registry, Redpanda automatically updates the Iceberg table schema to match the new schema.