build: Manually pull some RTD Context. (#2236)

See https://about.readthedocs.com/blog/2024/07/addons-by-default/ for details but
essentially RTD is changing how it's building docs and this will let us handle the
change gracefully.

docs/conf.py

@@ -74,3 +74,14 @@
 # Set the DJANGO_SETTINGS_MODULE if it's not set.
 if not os.environ.get('DJANGO_SETTINGS_MODULE'):
    os.environ['DJANGO_SETTINGS_MODULE'] = 'settings.base'
+
+# -- Read the Docs Specific Configuration
+# Define the canonical URL if you are using a custom domain on Read the Docs
+html_baseurl = os.environ.get("READTHEDOCS_CANONICAL_URL", "")
+
+# Tell Jinja2 templates the build is running on Read the Docs
+if os.environ.get("READTHEDOCS", "") == "True":
+    if "html_context" not in globals():
+        html_context = {}
+    html_context["READTHEDOCS"] = True
+