Configuration file for dfc

Adding the ability to pass a configuration file to the DFC tool, similar to the existing custom-mappings.yaml, or as an extension of it would be really useful. This configuration file would allow users to define common properties that can be easily accessed.
As more customers adopt this tool, various teams within organizations will be using it. A configuration file that pre-populates essential parameters, such as --org-name (which many users may not know), or even better defining a private registry for customers who mirror or have a pull-through cache set up, would significantly streamline the user experience. This enhancement would help ensure that all teams can run the tool effectively without needing to manually configure these common parameters.

Start by examining the existing custom-mappings.yaml handling and the CLI options mentioned in the issue, including --org-name and private registry settings. Define the configuration format and precedence rules before identifying the relevant parsing and execution entry points. Done means common parameters can be supplied through a configuration file and the documented CLI behavior remains clear.