doc: enable ReadTheDocs addon management

Up to now ReadTheDocs has been injecting code when building on their
platform. This includes for instance improvements for the search function.

To maintain the current output ReadTheDocs requires setting html_baseurl
and html_context in conf.py.

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

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

doc/conf.py

@@ -21,6 +21,12 @@ from subprocess import check_output
 # Get Sphinx version
 major, minor, patch = sphinx.version_info[:3]
 
+# 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":
+    html_context["READTHEDOCS"] = True
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the