Allow isUnique mutation on standard field (#17120)

# Introduction
As we've just
[identified](https://github.com/twentyhq/twenty/pull/16981) the standard
field metadata in production we can not enable the is unique comparison
even for standard entities

packages/twenty-server/src/engine/metadata-modules/flat-field-metadata/constants/flat-field-metadata-editable-properties.constant.ts

@@ -21,7 +21,6 @@ export const FLAT_FIELD_METADATA_EDITABLE_PROPERTIES = {
     'label',
     'options',
     'settings',
-    //TODO :  uncomment once universal identifier on standard fields is migrated
-    // 'isUnique', // not editable for standard fields with standard unique constraint
+    'isUnique',
   ],
 } as const satisfies Record<'standard' | 'custom', (keyof FlatFieldMetadata)[]>;