Add shift option to moving_avg aggregation (#4140)

Addresses elastic/elasticsearch#44360

(cherry picked from commit 6e121ef)

Author: Mpdreamz

src/Nest/Aggregations/Pipeline/MovingFunction/MovingFunctionAggregation.cs

@@ -12,6 +12,9 @@ public interface IMovingFunctionAggregation : IPipelineAggregation
 
 		[DataMember(Name ="window")]
 		int? Window { get; set; }
+
+		[DataMember(Name ="shift")]
+		int? Shift { get; set; }
 	}
 
 	public class MovingFunctionAggregation
@@ -26,6 +29,8 @@ public MovingFunctionAggregation(string name, SingleBucketsPath bucketsPath)
 
 		public int? Window { get; set; }
 
+		public int? Shift { get; set; }
+
 		internal override void WrapInContainer(AggregationContainer c) => c.MovingFunction = this;
 	}
 
@@ -35,9 +40,13 @@ public class MovingFunctionAggregationDescriptor
 	{
 		string IMovingFunctionAggregation.Script { get; set; }
 		int? IMovingFunctionAggregation.Window { get; set; }
+		int? IMovingFunctionAggregation.Shift { get; set; }
 
 		public MovingFunctionAggregationDescriptor Window(int? windowSize) => Assign(windowSize, (a, v) => a.Window = v);
 
 		public MovingFunctionAggregationDescriptor Script(string script) => Assign(script, (a, v) => a.Script = v);
+
+		public MovingFunctionAggregationDescriptor Shift(int? shift) => Assign(shift, (a, v) => a.Shift = v);
+
 	}
 }

src/Tests/Tests/Aggregations/Pipeline/MovingFunction/MovingFunctionAggregationUsageTests.cs

@@ -21,7 +21,7 @@ namespace Tests.Aggregations.Pipeline.MovingFunction
 	 *
 	 * Be sure to read the Elasticsearch documentation on {ref_current}/search-aggregations-pipeline-movfn-aggregation.html[Moving Function Aggregation]
 	 */
-	[SkipVersion("<6.4.0", "Introduced in Elasticsearch 6.4.0+")]
+	[SkipVersion("<7.4.0", "Shift option introduced in 7.4.0+")]
 	public class MovingFunctionAggregationUsageTests : AggregationUsageTestBase
 	{
 		public MovingFunctionAggregationUsageTests(ReadOnlyCluster cluster, EndpointUsage usage) : base(cluster, usage) { }
@@ -50,6 +50,7 @@ public MovingFunctionAggregationUsageTests(ReadOnlyCluster cluster, EndpointUsag
 						{
 							buckets_path = "commits",
 							window = 30,
+							shift = 0,
 							script = "MovingFunctions.unweightedAvg(values)"
 						}
 					}
@@ -69,6 +70,7 @@ public MovingFunctionAggregationUsageTests(ReadOnlyCluster cluster, EndpointUsag
 					.MovingFunction("commits_moving_avg", mv => mv
 						.BucketsPath("commits")
 						.Window(30)
+						.Shift(0)
 						.Script("MovingFunctions.unweightedAvg(values)")
 					)
 				)
@@ -84,6 +86,7 @@ public MovingFunctionAggregationUsageTests(ReadOnlyCluster cluster, EndpointUsag
 					&& new MovingFunctionAggregation("commits_moving_avg", "commits")
 					{
 						Window = 30,
+						Shift = 0,
 						Script = "MovingFunctions.unweightedAvg(values)"
 					}
 			};