The standard workflow in config mode scripts is to (1) obtain the config information in the form of the config dictionary (get_config_dict) (2) merge in any defined default values for those leaf node values not set by config, and pass the resulting dictionary as argument to the next stages (verify; generate; apply).

It is however useful on occasion to be able to check in a later stage (verify) whether a given value had originally been set by the user, or simply merged in by default. Carry over this missing information in the config dict, and add a boolean test 'from_defaults' to check if a given path was originally set by user (False) or only merged in by defaults (True).

Note that this will be implemented for get_config_dict(.., with_defaults=True), which does the merging of defaults automatically, after T5228, as used in T5308.