Add a way to track the source of configuration parameters

[chshersh]

It's extremely useful for diagnostic purposes to understand where a particular setting came from:

• Default static configuration
• Configuration file
• Environment variables
• CLI options

Prior art:

• trial: The trial package provides a data structure that allows tracking the source of config and printing this info to terminal

We would like to have this feature in Iris. This ticket is mostly about gathering ideas and designing the implementation.

Any ideas are welcome!