Deprecate factor on DateHistogramAggregation

Closes #2124

Author: russcam

src/Nest/Aggregations/Bucket/DateHistogram/DateHistogramAggregation.cs

@@ -30,6 +30,7 @@ public interface IDateHistogramAggregation : IBucketAggregation
 		[JsonProperty("time_zone")]
 		string TimeZone { get; set; }
 
+		[Obsolete("Deprecated. Will be removed in the next major version")]
 		[JsonProperty("factor")]
 		int? Factor { get; set; }
 
@@ -58,7 +59,7 @@ public string Format
 		{
 			get
 			{
-				return !string.IsNullOrEmpty(_format) && 
+				return !string.IsNullOrEmpty(_format) &&
 					!_format.Contains("date_optional_time") &&
 					ExtendedBounds != null
 					? _format + "||date_optional_time"
@@ -69,7 +70,10 @@ public string Format
 
 		public int? MinimumDocumentCount { get; set; }
 		public string TimeZone { get; set; }
+
+		[Obsolete("Deprecated. Will be removed in the next major version")]
 		public int? Factor { get; set; }
+
 		public string Offset { get; set; }
 		public HistogramOrder Order { get; set; }
 		public ExtendedBounds<DateTime> ExtendedBounds { get; set; }
@@ -144,6 +148,7 @@ public DateHistogramAggregationDescriptor<T> MinimumDocumentCount(int minimumDoc
 
 		public DateHistogramAggregationDescriptor<T> TimeZone(string timeZone) => Assign(a => a.TimeZone = timeZone);
 
+		[Obsolete("Deprecated. Will be removed in the next major version")]
 		public DateHistogramAggregationDescriptor<T> Interval(int factor) => Assign(a => a.Factor = factor);
 
 		public DateHistogramAggregationDescriptor<T> Offset(string offset) => Assign(a => a.Offset = offset);
@@ -161,4 +166,4 @@ public DateHistogramAggregationDescriptor<T> ExtendedBounds(DateTime min, DateTi
 
 		public DateHistogramAggregationDescriptor<T> Missing(DateTime missing) => Assign(a => a.Missing = missing);
 	}
-}
+}