[refactor] Cannot have code changes in `auto_config.cpp` - will be overriden

[AlbertoEAF]

I just found out this file helpers/parameter_generator.py, which states at the beginning:

This script generates LightGBM/src/io/config_auto.cpp file
with list of all parameters, aliases table and other routines
along with parameters description in LightGBM/docs/Parameters.rst file
from the information in LightGBM/include/LightGBM/config.h file.

meaning all the changes in config_auto that are done currently in fairgbm need to be moved out of there to the original LightGBM/include/LightGBM/config.h file.

[AndreFCruz]

I'll leave here a couple of required changes to the configs:

and:

[AndreFCruz]

Update: all code changes have been ported to the config.h file (we still need if there are any errors when parsing/compiling it to the generated config_auto.cpp).

[GoncaloArs]

FairGBM parameters need to be defined in order for this task to be completed.