Skaffold should provide a stopEvent

[briandealwis]

When Skaffold is started, it provides a start-event (though not programmatically identifiable):

{
  "result": {
    "timestamp": "2020-01-30T16:56:47.256487Z",
    "event": {
      "metaEvent": {
        "entry": "Starting Skaffold: &{Version: ConfigVersion:skaffold/v2alpha3 GitVersion: GitCommit: GitTreeState: BuildDate: GoVersion:go1.13.4 Compiler:gc Platform:darwin/amd64}"
      }
    }
  }
}

But there's no explicit tear-down event. It would be useful for any clients to differentiate between the socket being dropped for some reason (unlikely as it is) vs Skaffold being stopped.