Agent: Edit Job backend (#700)

* added stepInfo for editing jobs/steps

* added schedules to history requests

* added alerts and schedules to history

* formatting

* code review comments

* removed smo import

src/Microsoft.SqlTools.ServiceLayer/Agent/Contracts/AgentScheduleInfo.cs

@@ -64,5 +64,6 @@ namespace Microsoft.SqlTools.ServiceLayer.Agent.Contracts
         public int JobCount { get; set; }
         public DateTime ActiveEndDate { get; set; }
         public Guid ScheduleUid { get; set; }
+        public string Description { get; set; }
     }
 }