devel: apidoc generated ref documentation is not accessible from index pages

For each documented swh python packages, the apidoc generated ref doc seems to be generated properly (accessible via https://docs.softwareheritage.org/py-modindex.html) but there is no link from the packages' main index page. For example https://docs.softwareheritage.org/devel/swh-core/index.html#reference-documentation does not provide a link to https://docs.softwareheritage.org/devel/apidoc/swh.core.html#module-swh.core