expose status field as part of journey/end and step/end

[vigneshshanmugam]

• Right now we expose the status -> succeeded, failed as part of the payload field which is not searchable.
• We move that to the journey and step schema which would make things easier for the heartbeat and also for the UI to query these fields.

{
    "type": "journey/end"
   "journey": {
       "name": "blah",
       "id": "blah",
       "status": "failed"
    },
    "error": {}
}

{
    "type": "step/end"
   "step": {
       "name": "blah",
       "id": "blah",
       "status": "failed"
    },
    "error": {}
}