cubicweb #17254012 Allow to set version from vcs and stop expect it from __pkginfo__ [open]

Using https://pypi.org/project/setuptools-scm/ allow to manage version from mercurial tags and allow to work with intermediate versions.

cubicweb currently read cubes versions from __pkginfo__.py, to make this work it should read them from pkg_resources API instead.

Also we must check that migration system doesn't break with intermediate versions like "X.Y.Z.devP+hgHASH"

priorityimportant
typeenhancement
done in<not specified>
closed by<not specified>