[codespell] Add tox target and configuration for codespell

Continuing the work of @JayF in other repos.

Adds a tox target for codespell, `tox -e codespell`. Can optionally
be run as `tox -e codespell -- -w` to get automatic spelling fixes
applied where appropriate. Adds small amounts of configuration to
setup.cfg, including an ignore list of words.

Related Bug: https://bugs.launchpad.net/ironic-python-agent/+bug/2047654

Change-Id: I284045ee9dfb51eee59a0442abda657c74abed05

setup.cfg

@@ -47,3 +47,9 @@ json_rpc =
     keystoneauth1>=4.2.0 # Apache-2.0
     os-service-types>=1.2.0  # Apache-2.0
     oslo.service!=1.28.1,>=1.24.0 # Apache-2.0
+
+[codespell]
+quiet-level = 4
+# Words to ignore:
+# crypted: Valid in some contexts, e.g. "crypted password"
+ignore-words-list = crypted

tox.ini

@@ -73,3 +73,12 @@ allowlist_externals = make
 commands = sphinx-build -b latex doc/source doc/build/pdf
            make -C doc/build/pdf
 
+
+[testenv:codespell]
+description =
+  Run codespell to check spelling
+deps = codespell
+# note(adamcarthur): {posargs} lets us run `tox -ecodespell -- -w` to get codespell
+#             to correct spelling issues in our code it's aware of.
+commands =
+  codespell {posargs}