build: add configuration for black

pyproject.toml

+[tool.black]
+target-version = ["py38"]
+# TODO: Use extend-exclude as soon as Debian Bookworm is released.
+exclude = '''
+    ^/run\.py$
+    | ^/python/
+'''
+
+[tool.isort]
+profile = "black"

[David Trattnig]

@sumpfralle is there a "py39" target for Black already?

[Lars Kruse]

Yes, it should be available in the black version shipped with Debian Bullseye (which contains Python 3.9). I think, I just kept it here at the level specified as the minimum version for engine. Feel free to change it.