[feature request] Support for packages not in VCS to be handled by packagist.org

I have a build process for building stable .tar.gz and .zip files, which removes unnecessary files, not needed by composer based consumers of my library - such a test data, documentation etc.

I would also prefer users to use my own HTTP download server, then download from GitHub.

Please can you make it possible to register these repositories with packagist.org, to reduce any extra configuration by the consumer.

Start by reviewing Packagist's repository registration flow and how it records package sources. Define how a package without VCS hosting can register stable tar.gz and zip downloads from an external HTTP server, and consider the Composer consumer's resulting configuration as the completion criterion.

Written by the indexing model from the issue text.