Review relevance of existing tests and integrate more

[marota]

Add tests for grid2op_utils

[marota]

Current test sections to be reviewed
tests/unit_tests/test_EconomicDispatch.py ....... [ 25%]
tests/unit_tests/test_config.py ....... [ 48%]
tests/unit_tests/test_grid2op_import.py . [ 51%]
tests/unit_tests/test_load_coherence.py . [ 54%]
tests/unit_tests/test_load_prod_coherence.py .. [ 61%]
tests/unit_tests/test_main.py ....... [ 83%]
tests/unit_tests/test_output_processor.py ... [ 93%]
tests/unit_tests/test_solar_coherence.py . [ 96%]
tests/unit_tests/test_utils.py . [100%]