Add Julia Lister for listing Julia Packages

This module introduce Julia Lister. It retrieves Julia packages origins from the Julia General Registry, a Git repository indexing Julia packages.

It use Dulwich to get the Julia General Registry Git repository up to date. With the information contained in Registry.toml we build a path for each package and read its Package.toml definition which contains the related repository url.

Julia packages are Git repositories hosted on Github and using Github release features to manage and distribute Julia packages.

Refs. swh/meta#5065