Add support for Packages

[JustAnotherArchivist]

Feature description: https://github.com/features/packages

Docs: https://docs.github.com/en/packages

Introduction blog post: https://github.blog/2019-05-10-introducing-github-package-registry/

Random examples (all from a search for 'random'):

• npm: https://github.com/devsnek/fuzzy/packages/11085
• Containers and Docker:
  • There are 'containers' and 'Docker' on the search list as of right now. Maybe the latter only support Docker while the former are more generic? I haven't looked into it, to be honest. One obvious difference is that the former are hosted under ghcr.io while the latter are on docker.pkg.github.com, it seems.
  • Container: https://github.com/dedickinson/demo-api-random-python/pkgs/container/demo-api-random-python%2Fdemo-api-random
  • Container with old untagged versions: https://github.com/ori-rando/wotw-server/pkgs/container/wotw-server/versions
  • Docker: https://github.com/michaelwittmann/docker_simulation_pipeline_example/packages/516186
• NuGet: https://github.com/linksplatform/Random/packages/43326
• Maven: https://github.com/grunka/xorshift/packages/24609
  • Edge case: https://github.com/igabaydulin/github-registry-maven-stub/packages/11170 has no assets
  • The documentation also mentions a 'Gradle repository', but er yeah, about that... I couldn't find any example marked as 'Gradle' on the search.
• RubyGems: https://github.com/Mifrill/rollout_percentage/packages/502440

[JustAnotherArchivist]

I'm not sure whether it might be possible for a repository to have packages of more than one type.

Packages might exist that are not associated with a repository since the docs explain 'connecting a repository to a package'.

[Arkiver2]

Looks like this should already be supported.

[JustAnotherArchivist]

Even the container/Docker images? Those aren't linked directly. The other ones have linked assets, so those might be fine. I'm unfamiliar with those tools though and how they fetch content. But I'm guessing the assets are the crucial part at least.

[Arkiver2]

The container/Docker images may be something for a separate Docker archiving project at some point.