Instruct to use ruff instead of flake8

[dchristidis]

documentation/docs/developer/style_guide.md

Lines 8 to 14 in 2251284

	# General Style
	Rucio follows [flake8](https://flake8.pycqa.org/en/latest/user/index.html) style, ([with exclusions listed here](https://github.com/rucio/rucio/blob/6f87396ff372eff25224341987568792457c016a/pyproject.toml#L86)).
	To use them to lint your code, run:
	```
	python{version} -m pip install flake8
	flake8 --extend-ignore {codes to ignore} /your/code/path
	```

We recently stopped using flake8.