Import and track data for packages that have a reproducible build

The data for these is useful.
See:
- overall https://reproducible-builds.org/
- for Java https://github.com/jvm-repo-rebuild/reproducible-central
- A list of "reproducibles", but this should be using a structured format https://github.com/jvm-repo-rebuild/reproducible-central
- See also buildspec files at https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/doc/BUILDSPEC.md and an example at https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/org/apache/maven/shared/archiver/maven-archiver-3.5.1.buildspec ( @hboutemy hey 👋 )