Feature: support Consul's Event API

Consul's Event API description...

> The event command provides a mechanism to fire a custom user event to an entire data-center. These events are opaque to Consul, but they can be used to build scripting infrastructure to do automated deploys, restart services, or perform any other orchestration action. Events can be handled by using a watch.

Docs:
https://www.consul.io/api-docs/event
https://www.consul.io/commands/event

I'm searching for more data on potential use cases but haven't found much so far. If you know of any please let me know in a comment. Thanks.

Start with Consul's Event API and event command documentation at the two linked URLs, then inspect hcat's existing Consul-related behavior. Define what supporting the Event API should cover, including a concrete use case, and verify that the resulting behavior can fire and handle the requested events.

Written by the indexing model from the issue text.