Add running state to datafeed stats (#5792) (#5794)

Co-authored-by: Steve Gordon <sgordon@hotmail.co.uk>

src/Nest/XPack/MachineLearning/Datafeed/DatafeedStats.cs

@@ -23,6 +23,12 @@ public class DatafeedStats
 
 		[DataMember(Name = "timing_stats")]
 		public DatafeedTimingStats TimingStats { get; internal set; }
+
+		/// <summary>
+		/// The running state for the datafeed. It is only provided if the {dfeed} is started.
+		/// </summary>
+		[DataMember(Name = "running_state")]
+		public RunningState RunningState { get; internal set; }
 	}
 
 	[DataContract]

src/Nest/XPack/MachineLearning/Datafeed/RunningState.cs

@@ -0,0 +1,21 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Runtime.Serialization;
+
+namespace Nest
+{
+	/// <summary>
+	/// The running state for a datafeed once started.
+	/// </summary>
+	[DataContract]
+	public class RunningState
+	{
+		[DataMember(Name = "is_real_time")]
+		public bool IsRealTime { get; internal set; }
+
+		[DataMember(Name = "look_back_finished")]
+		public bool LoopBackFinished { get; internal set; }
+	}
+}