style: add configuration and Makefile for black, flake8, isort and codespell

.flake8

+[flake8]
+max-line-length = 99
+exclude = config/, python/, src/rest/, .tox/
+ignore = E121,E123,E126,E203,E226,E24,E704,W503,N802

Makefile

+SPELLING_PATHS = $(wildcard *.md) docs src
+SPELLING_EXCLUDE_FILENAME = .codespell-excludes
+SPELLING_IGNORE_WORDS_FILENAME = .codespell-ignore-words
+
+
+.PHONY: help
+help:
+	@echo "Supported targets:"
+	@echo "    lint            - verify code style"
+	@echo "    spelling        - check spelling of text"
+	@echo "    style           - apply automatic formatting"
+	@echo
+
+
+.PHONY: lint
+lint:
+	python3 -m flake8 .
+
+
+.PHONY: spelling
+spelling:
+	codespell \
+		--exclude-file "$(SPELLING_EXCLUDE_FILENAME)" \
+		--ignore-words "$(SPELLING_IGNORE_WORDS_FILENAME)" \
+		$(SPELLING_PATHS)
+
+.PHONY: style
+style:
+	python3 -m isort .
+	black .

pyproject.toml

+[tool.black]
+target-version = ["py38"]
+# TODO: Use extend-exclude as soon as Debian Bookworm is released.
+exclude = '''
+    ^/src/rest/
+    | ^/config/
+    | ^/python/
+    | ^/.tox/
+'''
+
+[tool.isort]
+py_version = 38
+profile = "black"
+# TODO: switch to "extend_skip", after Debian Bookworm is released
+skip = [
+    "config",
+    "node_modules",
+    "python",
+    "src/rest/",
+    ".git",
+    ".tox",
+]