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)
So just to double check, I ought to hard-code this to:

```ruby
GdsApi::Organisations.new('https://www.gov.uk')
```
?