[Backport master] Add architecture stats to cluster node stats (#5369)

* Add architecture stats to cluster node stats (#5338)

(cherry picked from commit e635a2b)

* Fix incorrect model for cluster stats (#5361)

(cherry picked from commit 0617626)

Author: stevejgordon

src/Nest/Cluster/ClusterStats/ClusterNodesStats.cs

@@ -177,6 +177,9 @@ public class ClusterOperatingSystemStats
 
 		[DataMember(Name = "pretty_names")]
 		public IReadOnlyCollection<ClusterOperatingSystemPrettyNane> PrettyNames { get; internal set; }
+
+		[DataMember(Name = "architectures")]
+		public IReadOnlyCollection<ArchitectureStats> Architectures { get; internal set; }
 	}
 
 	[DataContract]
@@ -255,4 +258,14 @@ public class ClusterProcessorStats
 		[DataMember(Name ="time_in_millis")]
 		public long TimeInMilliseconds { get; set; }
 	}
+
+	[DataContract]
+	public class ArchitectureStats
+	{
+		[DataMember(Name = "arch")]
+		public string Architecture { get; set; }
+
+		[DataMember(Name = "count")]
+		public int Count { get; set; }
+	}
 }

tests/Tests/Cluster/ClusterStats/ClusterStatsApiTests.cs

@@ -73,6 +73,14 @@ protected void Assert(ClusterNodesStats nodes)
 			nodes.OperatingSystem.AvailableProcessors.Should().BeGreaterThan(0);
 			nodes.OperatingSystem.AllocatedProcessors.Should().BeGreaterThan(0);
 
+			if (Cluster.ClusterConfiguration.Version.InRange(">=7.12.0"))
+			{
+				nodes.OperatingSystem.Architectures.Should().NotBeNull();
+				nodes.OperatingSystem.Architectures.Count.Should().BeGreaterThan(0);
+				nodes.OperatingSystem.Architectures.First().Architecture.Should().NotBeNullOrEmpty();
+				nodes.OperatingSystem.Architectures.First().Count.Should().BeGreaterThan(0);
+			}
+
 			nodes.OperatingSystem.Names.Should().NotBeEmpty();
 
 			if (Cluster.ClusterConfiguration.Version >= "6.8.0")