Support Sensu Go agent event API

Hey!

I'd like to get the Kapacitor sensu event handler to support the new Sensu Go agent event API, instead of the older client tcp socket. The tcp socket is available right now in the Sensu Go agent, but for compatibility only, it'll be deprecated and then removed at some point.

So in preparation for that eventuality I'd like to get the Kapacitor sensu handler updated to use the event API. I'm hoping to be able to spin up a PR on my own for review and see if we can get this update into kapacitor.

What's the best way forward here? Should I spin up a new sensu-go handler or enhance the existing sensu handler? A new handler is cleaner, but updating the existing handler with a configuration option to switch between client socket and sensu-go event api via a config option would be an easier migration for existing users of the sensu handler.

Start by locating Kapacitor's existing Sensu handler and reviewing how it currently uses the Sensu client TCP socket. Then compare the required Sensu Go agent event API and determine whether compatibility belongs in the existing handler or a new one; done means the handler supports the newer API with a clear migration path.

Written by the indexing model from the issue text.