Provide CloudEvents when workload(s) are scaling in/out

[tomkerkhove]

Proposal

Event Types

• keda.workload.scaling.scaleout.v1
• keda.workload.scaling.scalein.v1

Payload:

{
    "specversion" : "1.0",
    "type" : "keda.workload.scaling.scaleout.v1",
    "subject" : "/{kubernetes-cluster-name}/{namespace}/workload/{resource-name}/",
    "time" : "2018-04-05T17:31:00Z",
    "datacontenttype" : "application/json",
    "data" : {
      "scaleTarget": {
         "name": "sample-workload",
         "apiVersion": "Deployment",
         "kind": "apps/v1",
      },
      "replicas": {
         "old": 1,
         "new": 4
      }
   }
}

Use-Case

Allow end-users to get notified when a workload is actively scaling out/in.

Anything else?

Given we rely on the HPA, we need to find a way to integrate with it to leverage this.

Relates to #479