Add new style icons to subscriptions

[johncowen]

Description

One thing I wanted to do with the subscriptions re-design was to add some icons back into each row denoting whether the subscriptions is connected or not. It would look similar to our Zone listings that have universal/kubernetes icons. I was thinking of using the VitalsIcon (https://kong.github.io/icons/?q=vitals) in green and the Remove Icon (https://kong.github.io/icons/?q=remove) which looks like a line, in grey.

Didn't quite get around to doing that, but we should circle back and do that.

edit: P.S. I also think we should add a single sentence explanation at the top of these tables to explain what subscriptions (aka XDS or KDS Connections) are.