first attempt - select filter still not working

Closes #3498258

config/schema/views_csv_source.views.schema.yml

@@ -65,6 +65,9 @@ views.query.views_csv_source_query:
     headers:
       type: string
       label: 'Headers'
+    header_index:
+      type: integer
+      label: 'Header offset'
     request_method:
       type: string
       label: 'Request method'