Refs #34140 -- Added configurations to run blacken-docs linter and adjusted docs.

This adds:
- GitHub actions,
- tox configuration,
- pre-commit hook, and
- makefile rules
to run blacken-docs linter.

Co-authored-by: David Smith <smithdc@gmail.com>

.github/workflows/docs.yml

@@ -38,3 +38,24 @@ jobs:
         run: |
           cd docs
           sphinx-build -b spelling -n -q -W --keep-going -d _build/doctrees -D language=en_US -j auto . _build/spelling
+
+  blacken-docs:
+    runs-on: ubuntu-latest
+    name: blacken-docs
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+      - run: python -m pip install blacken-docs
+      - name: Build docs
+        run: |
+          cd docs
+          make black
+          RESULT=`cat _build/black/output.txt`
+          if [ "$RESULT" -gt 0 ]; then
+              echo "💥 📢 Code blocks in documentation must be reformatted with blacken-docs 📢 💥"
+          fi;
+          exit $RESULT