build: Manually pull some RTD Context. (#217)

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

@@ -106,5 +106,14 @@
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ['_static']
 
+# -- 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", "")
 
-# -- Extension configuration -------------------------------------------------
+# 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
+
+# -- Extension configuration -------------------------------------------------