Make the contextpath included in DocumentsResource from cmsrest configurable from the mount that belongs to the HstLink

If we want to support multi-webapp, we need to be able to set a different context path per environment / host / mount

This is also needed for the channel manager.

Currently, it is something like:

document.setUrlContainsContextPath(link.getMount().getVirtualHost().isContextPathInUrl());

This is not useful : The contextpath should always be included from cms calls to the HST. It is much more useful to know which contextpath