Stop overwriting the routes.yaml file

The current implementation of this module overwrite routes.yaml with the exact settings needed by PuppetDB. If a user already has a routes.yaml file that is managing other things besides the the facts terminus, their settings will be blown away.

We should handle this more gracefully. It ought to be pretty simple to put together a yaml module that had a resource type for dealing with an individual yaml setting. If we did that, then the PuppetDB module could use that to set only the relevant settings without overriding any existing settings.

Start by locating the PuppetDB module code that writes routes.yaml and inspect how its current settings are assembled. Define the YAML resource behavior around individual settings, then verify that PuppetDB's required facts terminus settings are managed without overwriting unrelated user settings in routes.yaml.