CI and code formatting: add isort and flake8 checks to CI pipeline

[priitlatt]

Implement automatic code In order to make code review process easier.

Added two automatic checks to CI pipeline:

• flake8 code fromatting checks with flake8_quotes, flake8_commas and pep8-naming extensions,
• isort imports ordering checks.

Existing codebase was updated with minimal changes to pass the checks.

[priitlatt]

• Passed flake8 check
• Passed isort check