Add an enforcer rule to give a warning if the "allTests" option is set, but public-repos is not.

As per Paul's suggestion

Maybe we can add an enforcer rule to give a warning if the "allTests" option is set, but public-repos is not.

in
https://issues.jboss.org/browse/JBPAPP-10020?focusedCommentId=12726564&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12726564