Expose license terms over API

In order that users of content can see what license terms apply to a specific resource, support an API that discovery/A-Z/link resolver interfaces can cal and get a JSON representation of the relevant agreement(s)+license back for public facing properties

Options for API are either to make the data available via a public URL, or via an Edge API. The former is preferred by the development team for simplicity unless there is a compelling reason to do this as an Edge API