Add an endpoint to retrieve the latest build artifact for a branch

Zendesk: https://gitlab.zendesk.com/agent/tickets/16085

What I would like to have is an API - something like:

GET /projects/:id/builds/latest/:branch-name/artifacts

Or something that will allow me to pull the most recent successful build artifact per branch. Then, automation tools such as Chef can pull down the artifact and act on it.