OpenAPI: fix group settings documentation

the OpenAPI docs should really be improved, but nobody seems interested
enough to sponsor this work

Fixes #1141

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

openapi/openapi.yaml

@@ -6172,6 +6172,8 @@ components:
           description: 'Maximum total data transfer as MB'
         filters:
           $ref: '#/components/schemas/BaseUserFilters'
+        filesystem:
+          $ref: '#/components/schemas/FilesystemConfig'
     Role:
       type: object
       properties: