Supports managing addon components in hub cluster #54
Description
currently a typical addon consists of (1) addon manager (2) addon agent. in which the addon manager is sometimes not only responsible for delivering resources to the managed clusters upon addons' enablment but also some server components in the hub clusters paired with the agent components. e.g. in the cluster-proxy addon, we're deploying anp servers upon global addon enablement which the addon agent will be connecting.
in the long term, the addon framework should help the addon developers to easily manage the components in the hub.