[FEATURE] Rename power_grid_model/auxiliary directory name, power_grid_model/main_core source file names

[Jerry-Jinfeng-Guo]

Currently under the power_grid_model/auxiliary directory, there live source files primarily for input / update /output related functionalities. auxiliary is a poor choice that not only reflects nothing of the purpose, but also can be misleading.

Proposal:
power_grid_model/auxiliary to power_grid_model/data_handling, power_grid_model/data_managing or even power_grid_model/data

Currently under power_grid_model/main_core, input.hpp, output.hpp, update.hpp and topology.hpp live. There are source files elsewhere same names. While this is acceptable, the contents of the four source are actually not truly reflected from their names.

Proposal:
power_grid_model/main_core/input.hpp to power_grid_model/main_core/input_handling.hpp, power_grid_model/main_core/input_managing.hpp, power_grid_model/main_core/input_impl.hpp or less uniform power_grid_model/main_core/input_to_model.hpp

power_grid_model/main_core/output.hpp to power_grid_model/main_core/output_handling.hpp, power_grid_model/main_core/output_managing.hpp, power_grid_model/main_core/output_impl.hpp or less uniform power_grid_model/main_core/output_result.hpp

power_grid_model/main_core/update.hpp to power_grid_model/main_core/update_handling.hpp, power_grid_model/main_core/update_managing.hpp, power_grid_model/main_core/update_impl.hpp or less uniform power_grid_model/main_core/update_model.hpp

power_grid_model/main_core/topology.hpp to power_grid_model/main_core/topology_handling.hpp, power_grid_model/main_core/topology_managing.hpp, power_grid_model/main_core/topology_impl.hpp or less uniform power_grid_model/main_core/topologize.hpp