Add flake8 extensions to linter CI workflow

[itrushkin]

This pull request contains:

• Including installation of flake8 extensions
• Making linter workflow fail on any non-ignored (see setup.cfg) error.
• Removing linter rules specified directly in workflow code. All rules have already been specified in setup.cfg file in the repository root.
• Fixing all linter errors

Tested the behavior locally via act.

[itrushkin]

New flake8 rules have been applied. I will convert this to a draft and fix all the issues here.

[igor-davidyuk]

Great, thank you!
One thing that I would do is separate this into two PRs.
One will contain changes to CI and another one with linter highlited fixes.

[itrushkin]

@igor-davidyuk It seems that CI changes affect GitHub actions immediately. I had linter errors after enabling the extensions, thus I had to fix them in the same pull request.

[igor-davidyuk]

@igor-davidyuk It seems that CI changes affect GitHub actions immediately. I had linter errors after enabling the extensions, thus I had to fix them in the same pull request.

Yeah, I thought it was the case. We could Merge a PR with fixes first to avoid this problem 🤣
But this is not that important, one combined PR is ok too.