Monitor still uses v0 Sparkplug notify interface

[amrc-benmorrow]

Once #560 and #561 are merged the Monitor will be the only service still using the old Sparkplug change-notify. It would be good to remove this; there are two uses:

• The central monitor watches for edge clusters and does a lot of dodgy stuff to find an edge monitor address. This could be tidied up altogether and use notify/v2 to track edge clusters. Ideally we'd want a link config entry to link monitor to cluster.
• The edge monitor watches the config file for each edge agent. Given the current state of the libraries it would be cleaner to have the EA do this itself. Originally I thought this would be pushing too much work on the Agent but with notify/v2 it's straightforward.

The monitor is also the only remaining use of sparkplug-app, using it to do the actual monitoring, but this is probably required.