Move flake8 settings to setup.cfg

[MorrisNein]

It is needed, since pep8speaks ignores setup.cfg file while the section flake8 is duplicated in both it and .pep8speaks.yml

[pep8speaks]

Hello @MorrisNein! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file meta_automl/data_preparation/dataset/__init__.py:

Line 1:1: F401 '.dataset_base.DatasetBase' imported but unused Line 1:1: F401 '.dataset_base.DatasetData' imported but unused Line 1:1: F401 '.dataset_base.DatasetIDType' imported but unused Line 1:1: F401 '.dataset_base.TabularData' imported but unused Line 1:1: F401 '.dataset_base.TimeSeriesData' imported but unused Line 2:1: F401 '.custom_dataset.CustomDataset' imported but unused Line 2:1: F401 '.custom_dataset.DataNotFoundError' imported but unused Line 3:1: F401 '.openml_dataset.OpenMLDataset' imported but unused Line 3:1: F401 '.openml_dataset.OpenMLDatasetIDType' imported but unused Line 4:1: F401 '.time_series_dataset.TimeSeriesDataset' imported but unused

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (cd85fc3) 30.29% compared to head (2238abe) 30.29%.

:exclamation: Current head 2238abe differs from pull request most recent head 9f9ae8c. Consider uploading reports for the commit 9f9ae8c to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #92 +/- ## ======================================= Coverage 30.29% 30.29% ======================================= Files 56 56 Lines 2340 2340 ======================================= Hits 709 709 Misses 1631 1631 ```

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