Getting and Setting Library Metadata

[radeusgd]

Pull Request Description

Implements the endpoint for getting library metadata, extending it with the ability to also fetch metadata for published libraries.

As it was needed for better testing, the endpoint setting metadata is also implemented.

Important Notes

• It changes the API, but since it was not yet being used, it is not marked as a breaking change.
• While such possibility is advertised in the documentation, the endpoint does not look for cached manifests of published libraries. That is because manifest caching is not yet implemented - once caching is implemented (probably around Downloading and Installing Libraries in the Package Manager #1772 when dependency downloading will be implemented), this should also be added.
• It also updates the API of library/create to use a Contact type for authors and maintainers, as the original API was not compatible with the config format - by mistake. Since this endpoint is not yet being used, the change also should not be breaking.

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the Scala, Java, and Rust style guides.
• All documentation and configuration conforms to the markdown and YAML style guides.
• All code has been tested where possible.