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)
These lines should probably be using `fetch`. If for some reason the `:title` key doesn't exist, we'd prefer it to fail noisily here rather than as part of an API call (or worse to have it succeed with unexpected data).