[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)
I'd prefer this to be repeated such that the code under test is exercised in the test rather than the setup.