tox: Add sphinx environments to check sane doc build
Enable to check package documentation can be built without producing sphinx warnings.
The sphinx
environment is designed to be used in continuous integration
in order to prevent breaking documentation build when committing changes.
The sphinx-dev
environment is designed to be used inside a full swh
development environment.
Related to T3258
I also added a commit to ensure tox
can be successfully executed
in that template module and another commit to fix a duplicated
reference in the sample doc.
Migrated from D5610 (view on Phabricator)