Log config to console for debugging purposes

[lannonbr]

It was brought up that printing out the resolved config would be useful to verify that a config was properly configured. This could be a console.log call in a node app using source-configs, but given many use cases include secrets like database passwords, it could be fine when working locally but dangerous if this is running in a production environment where someone who has access to the logs can view all of the credentials.

Instead, I suggest two features:

1. The ability to declare a config setting as a secret from a config schema.
2. A print function that prints out the resolved config in a formatted fashion. If it sees a config field that was set in the schema as a secret, it could mask it out like **** so one knows it was set but not defined.

As well it was mentioned the masking of a setting could be dependent on the environment it is in, so in dev / staging you could let the secrets be printed out, but not for production. We could either have a toggle for this within the print function or set it based upon the NODE_ENV environment variable.