[docs] try to enable need_pdf in .yfm

Author: blinkov

ydb/docs/.yfm

@@ -17,6 +17,7 @@ docs-viewer:
     id: GTM-W7ZBL4X
   github-url-prefix: https://github.com/ydb-platform/ydb/tree/main/ydb/docs
   unrestrict-revision-access: true
+  need_pdf: true
 
   logo-options:
     url: