Add a makefile for building debian packages This allow building debian source package from sdist. This is cleaner than building from hg clone because we ensure to only include what's listed in sdist MANIFEST.in in upstream tarball. The deb-zip target allow to build a zip for the source package, suitable as input of https://jenkins.intra.logilab.fr/job/pkg-from-dsc The deb target build the binary packages using sbuild.

remove debian/watch

This version should bring Python3 compatibility.

We refresh setup.py and __pkginfo__.py using CubicWeb 3.23 skeleton
which is Python3 compatible and still use the legacy layout.

so that pkg_resources can find the package when using a new-style cube

Use pybuild

This is expected for proper caching and will be made mandatory by cubicweb's
722690d7ae28

Closes #16347705