Notify finder api on publish

https://www.pivotaltracker.com/story/show/67303352

When a document is published the publisher sends a JSON blob of the document's attributes to the Finder API so it can be indexed for the front-end.

Both the endpoint and the JSON format are subject to change but probably not much.

Apart from the automated tests I've confirmed the API received the POST, no more local testing can be done until the receiving side is built.