Add additional metadata to Sensu alerts

[mdelaney]

Sensu supports the addition of arbitrary metadata along with check results. This can be extremely using on the Sensu side for everything from alert filtering to triggering some automatic remediation to showing a simple playbook link.

Right now sending an alert to Sensu looks like:

|alert()
  // ...
  .sensu()
    .source('Kapacitor')
    .handlers('handler1-name', 'handler2-name')

What I'd like to be able to do is something like

var occurrences  = 3
var refresh = 3600
var playbook = 'link.to.my.playbook'

|alert()
  // ...
  .sensu()
    .source('Kapacitor')
    .handlers('handler1-name', 'handler2-name')
    .metadata(occurrences, playbook, refresh)

Which would add the following to the check result JSON sent to Sensu

{
    ...
    "occurrences": 3,
    "playbook": "link.to.my.playbook",
    "refresh": 3600,
    ...
}