Provide a mechanism to expose the default config file

Pattern Lab Node should provide a method to supply a consumer with the default `patternlab-config.json` file, https://github.com/pattern-lab/patternlab-node/blob/master/patternlab-config.json

Consumers can then mutate / save their own copy without having to rely on other copies of this file floating around editions / the CLI.

