Add config via setup.cfg

Is your feature request related to a problem? Please describe.

I'd like to use single setup.cfg file for many different linters/plugins/style checkers. Currently bandit requires to have special config for it and is not able to read setup.cfg.

Describe the solution you'd like

1. Check multiple different paths for config file by default
2. Implement proper parsing of setup.cfg (which is not YAML but more like INI-like format)

Example:

[isort]
# https://github.com/timothycrosley/isort/wiki/isort-Settings
line_length=119
case_sensitive=True
multi_line_output=7
force_single_line=True
default_section=THIRDPARTY

[bandit]
# https://bandit.readthedocs.io/en/latest/blacklists/index.html#
tests: ['B603']

[flake8]
# https://flake8.pycqa.org/en/latest/user/configuration.html
show_source = True

per-file-ignores =
    python/pypi/*: WPS300, WPS442

Describe alternatives you've considered
Separating configs which works, but clutters the workspace with files

Additional context
Basically the same as https://github.com/PyCQA/bandit/issues/212 (which was probably closed by mistake)

The issue names no files or tests. Start by locating Bandit's existing configuration-loading entry point, then examine how it searches for configuration and parses the current format. Done means supporting default config discovery across the requested paths and correctly reading the INI-like setup.cfg sections and values shown in the examples.