Adding took time to _msearch

Implements: elastic/elasticsearch#23767

Author: codebrain

src/Nest/Search/MultiSearch/MultiSearchResponse.cs

@@ -13,6 +13,8 @@ public class MultiSearchResponse : ResponseBase
 	{
 		public MultiSearchResponse() => Responses = new Dictionary<string, IResponse>();
 
+		public long Took { get; set; }
+
 		public IEnumerable<IResponse> AllResponses => _allResponses<IResponse>();
 
 		public override bool IsValid => base.IsValid && AllResponses.All(b => b.IsValid);

src/Nest/Search/MultiSearch/MultiSearchResponseFormatter.cs

@@ -36,6 +36,11 @@ public MultiSearchResponse Deserialize(ref JsonReader reader, IJsonFormatterReso
 						responses.Add(reader.ReadNextBlockSegment());
 					break;
 				}
+				else if (propertyName == "took")
+				{
+					response.Took = reader.ReadInt64();
+					continue;
+				}
 
 				reader.ReadNextBlock();
 			}

src/Tests/Tests/Search/MultiSearch/MultiSearchApiTests.cs

@@ -122,6 +122,8 @@ protected override LazyResponses ClientUsage() => Calls(
 
 		[I] public Task AssertResponse() => AssertOnAllResponses(r =>
 		{
+			r.Took.Should().BeGreaterThan(0);
+
 			r.TotalResponses.Should().Be(6);
 
 			var nvalidResponses = r.GetInvalidResponses();