Add information to the XML schema that states if an activity is being published by a secondary publisher.

This information is already published in the IATI Registry API, but the following use cases are not served by it:

• pulling all IATI Registry data together (e.g. into the datastore) and looking only at activities will not state whether or not this data is being published by a secondary publisher
• where a publisher publishes some data as the primary publisher and other data as the secondary publisher.

Propose adding an attribute to the reporting-org element:

• <reporting-org secondary-publisher="true"/>

In the course of consultation, it may be worth considering whether there is other Registry data that would also merit inclusion here (license in particular).