Implement vector usage (#4151)

(cherry picked from commit 31c0862)

Author: codebrain

src/Nest/XPack/Info/XPackUsage/XPackUsageResponse.cs

@@ -75,7 +75,7 @@ public class XPackUsageResponse : ResponseBase
 		public SecurityUsage Security { get; internal set; }
 
 		[DataMember(Name = "vectors")]
-		public XPackUsage Vectors { get; internal set; }
+		public VectorUsage Vectors { get; internal set; }
 
 		[DataMember(Name = "voting_only")]
 		public XPackUsage VotingOnly { get; internal set; }
@@ -90,6 +90,18 @@ public class XPackUsage
 		public bool Enabled { get; internal set; }
 	}
 
+	public class VectorUsage : XPackUsage
+	{
+		[DataMember(Name = "dense_vector_fields_count")]
+		public int DenseVectorFieldsCount { get; internal set; }
+
+		[DataMember(Name = "sparse_vector_fields_count")]
+		public int SparseVectorFieldsCount { get; internal set; }
+
+		[DataMember(Name = "dense_vector_dims_avg_count")]
+		public int DenseVectorDimensionsAverageCount { get; internal set; }
+	}
+
 	public class SecurityUsage : XPackUsage
 	{
 		[DataMember(Name = "anonymous")]

src/Tests/Tests/XPack/Info/XPackInfoApiTests.cs

@@ -100,7 +100,7 @@ [I] public async Task XPackUsageResponse() => await Assert<XPackUsageResponse>(X
 				r.Flattened.Should().NotBeNull();
 				r.DataFrame.Should().NotBeNull();
 				r.Vectors.Should().NotBeNull();
-        r.VotingOnly.Should().NotBeNull();
+				r.VotingOnly.Should().NotBeNull();
 			}
 		});
 	}