Push default ConfigAgent contents on facia startup

A vague copy of `PROD` `config.json` so that `facia` knows where to look straight away for each path.

This is mainly a dev environment nice to have.
Yes, but it's for `DEV`.
It's only used on the lookup by `facia` to see if it can serve the incoming path.

@mattosborn 's problem would have been partially solved the last day as he would have had one failing S3 request instead of two. :dancer: