fix: default onDeleteFilter implementation

Signed-off-by: Chris Laprun <[email protected]>

Author: metacosm

Diff for: operator-framework-core/src/main/java/io/javaoperatorsdk/operator/api/config/informer/InformerConfiguration.java

@@ -66,7 +66,9 @@ default boolean followControllerNamespaceChanges() {
    */
   SecondaryToPrimaryMapper<R> getSecondaryToPrimaryMapper();
 
-  Optional<OnDeleteFilter<? super R>> onDeleteFilter();
+  default Optional<OnDeleteFilter<? super R>> onDeleteFilter() {
+    return Optional.ofNullable(getInformerConfig().getOnDeleteFilter());
+  }
 
   <P extends HasMetadata> PrimaryToSecondaryMapper<P> getPrimaryToSecondaryMapper();