Add relations aggregates to sortable

Author: Marius

src/Http/Middleware/Decorators/AbstractDecoratorMiddleware.php

@@ -204,7 +204,13 @@ protected function getListNewContent(Request $request, array $content, array $co
         }
 
         $newContent['filterable'] = $this->decorator->getFilters();
-        $newContent['sortable'] = $indexedSortable ?? $this->decorator->getFilters();
+        $newContent['sortable'] = \array_merge(
+            $indexedSortable ?? $this->decorator->getFilters(),
+            \array_map(fn (string $rel): string => $rel .
+                $this->decorator::EXIST_SUFFIX, $this->decorator->getExistRelations()),
+            \array_map(fn (string $rel): string => $rel .
+                $this->decorator::COUNT_SUFFIX, $this->decorator->getCountRelations())
+        );
 
         return $newContent;
     }