[TO_DISCUSS] Publish manuals to the Publishing API

The Publishing API will eventually replace the Content API.

Before merging: 
- [ ] publish manual sections to the Publishing API.
- [ ] publish change notes to the Publishing API.
- [ ] augment the Publishing API payload with organisation info (this needs to be looked up against the Organisations API)
We've moved away from webmock and started using our own mock objects to assert on external interactions.

While this helper method is fine, we should consider the cost of inconsistency.