Fixes #6867 - Show system katello-agent installed

API Change: https://github.com/Katello/katello/pull/4515
You could use `Fields::Boolean` field type if the expected value is true/false and turn it into Yes/No. I consider it user-friendlier.
See example in https://github.com/Katello/hammer-cli-katello/blob/master/lib/hammer_cli_katello/repository_set.rb#L47