Ability to add new OS versions to metadata

[bwitt]

Similar to #973, but for adding new versions of existing OSes.

• add new versions of existing OSes that have versions listed. List would be hardcoded in the script.
• skip any OSes that do not list versions
• do not add any new OSes (since supporting a new OS will probably require a specific effort)

Have the https://github.com/voxpupuli/modulesync_config/blob/master/bin/clean-metadata script do this somehow

[bastelfreak]

Hi. https://github.com/voxpupuli/puppet_metadata is our authoritative source for all operating systems including their EoL date. And it can already parse a metadata.json. the idea is that it can add new operating systems. It can already add new versions for existing OSes in metadata.json. modulesync_config can then just call puppet_metadata for all repos.