add cosmiconfig to auth0-simulator

[dagda1]

It would be a better developer experience if the auth0 configuration was picked up automatically using cosmiconfig.

The config would be in the package.json file

  "auth0-simulator": {
    "domain": "localhost:4400",
    "clientId": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
    "scope": "openid profile email offline_access"
    // etc.
  }

Or in one of the loaders supported by cosmiconfig, .e.g. .js, .json, .yaml etc.