Expose external refreshes through the stats API (#3992)

Expose external refreshes through the stats API

(cherry picked from commit 92ee114)

Author: codebrain

src/Nest/CommonOptions/Stats/RefreshStats.cs

@@ -13,5 +13,17 @@ public class RefreshStats
 
 		[DataMember(Name ="total_time_in_millis")]
 		public long TotalTimeInMilliseconds { get; set; }
+
+		/// <summary>
+		/// Only valid for Elasticsearch 7.2.0 and above.
+		/// </summary>
+		[DataMember(Name ="external_total")]
+		public long ExternalTotal { get; set; }
+
+		/// <summary>
+		/// Only valid for Elasticsearch 7.2.0 and above.
+		/// </summary>
+		[DataMember(Name ="external_total_time_in_millis")]
+		public long ExternalTotalTimeInMilliseconds { get; set; }
 	}
 }