fix: #14495 Allow custom varchar attributes for customer grid

* As described in the issue, it does not make sense to use the backend-type for the UI-component data type, because those do not exist necessarily
* Changed it to frontend_input

Author: amenk

app/code/Magento/Customer/Ui/Component/Listing/Columns.php

@@ -171,7 +171,7 @@ public function updateColumn(array $attributeData, $newAttributeCode)
                     $component->getData('config'),
                     [
                         'name' => $newAttributeCode,
-                        'dataType' => $attributeData[AttributeMetadata::BACKEND_TYPE],
+                        'dataType' => $attributeData[AttributeMetadata::FRONTEND_INPUT],
                         'visible' => (bool)$attributeData[AttributeMetadata::IS_VISIBLE_IN_GRID]
                     ]
                 );