permit onion v3 authentication of Tor Browser

white list in `onion-grater`
    onion_client_auth_add:
          - '.+'

Thanks to @rustybird for the bug report!

https://phabricator.whonix.org/T996

etc/onion-grater-merger.d/30_whonix-default.yml

@@ -31,6 +31,8 @@
       - 'consensus/valid-after'
       - 'consensus/valid-until'
       - 'consensus/fresh-until'
+    onion_client_auth_add:
+      - '.+'
   confs:
     __owningcontrollerprocess:
   events: