Better surface moved Maven artifacts

Created by: varungandhi-src

If you search for r:^maven/org.apache.logging.log4j/log4j$, you get a repository match. However, if you navigate to the repository, you get a big "Empty repository" which is not helpful.

This may be because the package has been moved to log4j-core as noted on log4j's Maven page.

It would be nice if we surfaced this information in a better way. I'm not sure if npm can have the same issue or not.