GitLab

Update the build system to use pybuild.

The new binary package with Python 3 support is named
python3-cubicweb-skos according to current standards.
Python 2 package is also updated to use the proper namespace
and a transitional package has been introduced to handle
the migration.

Support for Python 3.8 is disabled as it is currently broken
in Debian unstable.

We currently ignore test/test_ccplugin.py as it requires
a PostgreSQL server. Running it through autopkgtest seems
like a more robust approach, but this remains to be
implemented.

Drop useless __pkginfo__.py symlink

But do not ship it in sdist.

Closes #17133722.

by adding them to the MANIFEST.in file