STYLE: run pre-commit filters on the repo
I noticed that `pre-commit` is used and ran `pre-commit run --all-files` which results in massive diffs, mostly because of `isort`.

I have added the correct `noqa` and `isort:skip` flags to the lines which needed it to function correctly with the current `.pre-commit-config.yaml`, such that the imports are correctly sorted now.

I also added `seed-isort-config` such that `setup.cfg` is parsed for `pre-commit` and fixed the formatting of `.pre-commit-config.yaml`.

~~Finally, there is `pandas/__init__.py` that is touched by `pre-commit run --all-files`, however, this has less trivial changes and might result in something breaking, so I don't dare to touch it.~~
It was because the `skip` entry in `[isort]` in `setup.cfg` is somehow ignored when running pre-commit and I can't figure out why (I will open an issue in the `isort` repo when it's clear that this will be merged). I have also deleted the other ignored files because I fixed the problems there. `pandas/core/api.py` needs to stay in `skip` because `isort` and `black` make conflicting edits.