conf: Prep for Sphinx context injection deprecation

Changes based on email from RTD:

    [Action required] Deprecation: Removal of Sphinx context injection at build time

And the following one blog post:

    https://about.readthedocs.com/blog/2024/07/addons-by-default/

conf.py

@@ -143,6 +143,15 @@
 
 html_theme = 'sphinx_rtd_theme'
 
+# Set canonical URL from the Read the Docs Domain
+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
+
 html_last_updated_fmt = '%B %d, %Y'
 
 # Theme options are theme-specific and customize the look and feel of a theme