Add job-state-transitions to Job History API

I understand. But Job history without state transitions would not be very useful. Im ok to do this change because we haven't done manual testing / performance analysis for this particular API yet. may be we can test - optimize. If it doesn't improve go back to how it was? let me know what you think. I have added this after a lot of deliberation. I think the information is very important. @sachinsudheendra was of the opinion that we should give state transitions out as separate api. I will let you take a call on this.