doc: enable ReadTheDocs addon management

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>