Enhance reporting of gpgkey issues in repo refresh

[mlandres]

Looking for gpg keys in repository repo-oss (15.6).
  gpgkey=https://cdn.opensuse.org/distribution/leap/15.6/repo/oss/repodata/repomd.xml.keyx
  gpgkey=https://cdn.opensuse.org/distribution/leap/15.6/repo/oss/repodata/repomd.xml.keyy

Zypp reports the URLs, but not what was found there and how it was consumed (new known key, already trusted, updating a trusted,...)