Comment 2 for bug 1824568

We should be able to do this relatively cheaply by looking at the telegraf haproxy relation. This is implemented in the haproxy charm as the statistics relation, the relevant portion of which seems to be https://pastebin.ubuntu.com/p/8qgrkJxKqq/. Obviously there's a little more to it than that as there are functions referenced there, but this should be the approach we take.