Update domain configuration so authors can read the extension config nodes

The current domain configuration allows users in the webmaster group to read ui extension configuration nodes. For page tool extensions that is fine. But authors should be able to read the document field extension nodes otherwise these will not work for authors.

Even if authors get permission to read all extension nodes the page tools do not appear for them in the channel manager. So it looks like that changing the group in /hippo:configuration/hippo:domains/ui-extensions/readonly from webmaster to everybody will fix this.