Create reference pages for configuration files used by Fuel

We need reference pages for the configuration files that Fuel uses to deploy the environment. These will be presented as the "File Reference" subsection in the fuel-docs documentation. Each page will contain:
- Name of the file, tagged with the file name and a -ref suffix (e.g. the astute.yaml page tag will be astute-yaml-ref
- Node(s) on which the file can be viewed and the full pathname
- Usage, showing the commands required to view the file and redeploy it if it is amended (e.g. fuel env -1 provisioning download, nailgun docker container)
- Description -- describe how the file is created, which process(es) use it, etc
- File layout -- display a sample file
- Fields -- describe the contents and use of each field/block in the file, what might be modified and when

Other information may be incorporated as appropriate.