Publish manuals, sections and change notes to the Publishing API

The Publishing API will eventually replace the Content API.

- [x] publish manualsto the Publishing API.
- [x] publish manual sections to the Publishing API.
- [x] publish change notes to the Publishing API.
- [x] augment the Publishing API payload with organisation info (this needs to be looked up against the Organisations API)
We have some work to do on making all of our things that deal with other systems more consistent. I'm happy to merge this for now and pick it up later if necessary as part of that work.