[STYLE] Sort imports

[jkowalleck]

as a developer i want all imports sorted, so i read and maintain them easily

---

proposal:

• have isort as a tool available in poetry-dev-env
• have isort configured -- see below
• have flake8 plugin flake8-isort` installed and setup in poetry-dev-env
• have isort applied to all python files (once)
• have the use of isort mentioned i the CONTRIBUTING docs

proposed isort config file .isort.cfg:

[isort]
## read the docs: https://github.com/timothycrosley/isort/wiki/isort-Settings
known_first_party = cyclonedx
skip_glob =
    build,dist,__pycache__,.eggs,*_cache
    .git,.tox,.venv,venv
    _OLD,_TEST,
    docs
combine_as_imports = true
default_section = THIRDPARTY
include_trailing_comma = true
line_length = 120
multi_line_output = 5