Implement formatter for GetCertificates response

This commit implements a formatter for the GetCertificatesResponse. The response JSON is an array of the format

[
  {
    "path" : "node01.crt",
    "format" : "PEM",
    "alias" : null,
    "subject_dn" : "CN=node01",
    "serial_number" : "<serial>",
    "has_private_key" : true,
    "expiry" : "2022-04-11T02:40:31.000Z"
  },
  {
    "path" : "ca.crt",
    "format" : "PEM",
    "alias" : null,
    "subject_dn" : "CN=Elastic Certificate Tool Autogenerated CA",
    "serial_number" :  "<serial>",
    "has_private_key" : false,
    "expiry" : "2022-04-11T02:40:31.000Z"
  }
]

In the event of an error, the response could be an object, so the formatter should handle this.

Author: russcam

src/Nest/CommonAbstractions/Response/DictionaryResponseBase.cs

@@ -20,7 +20,7 @@ public abstract class DictionaryResponseBase<TKey, TValue> : ResponseBase, IDict
 			EmptyReadOnly<TKey, TValue>.Dictionary;
 	}
 
-	internal class DictionaryResponseFormatterHelpers
+	internal class ResponseFormatterHelpers
 	{
 		internal static readonly AutomataDictionary ServerErrorFields = new AutomataDictionary
 		{
@@ -43,7 +43,7 @@ public TResponse Deserialize(ref JsonReader reader, IJsonFormatterResolver forma
 			while (reader.ReadIsInObject(ref count))
 			{
 				var property = reader.ReadPropertyNameSegmentRaw();
-				if (DictionaryResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
+				if (ResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
 				{
 					switch (errorValue)
 					{

src/Nest/CommonAbstractions/Response/ResolvableDictionaryProxy.cs

@@ -89,7 +89,7 @@ public TResponse Deserialize(ref JsonReader reader, IJsonFormatterResolver forma
 			while (reader.ReadIsInObject(ref count))
 			{
 				var property = reader.ReadPropertyNameSegmentRaw();
-				if (DictionaryResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
+				if (ResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
 				{
 					switch (errorValue)
 					{

src/Nest/Modules/SnapshotAndRestore/Repositories/GetRepository/GetRepositoryResponseFormatter.cs

@@ -15,7 +15,7 @@ public GetRepositoryResponse Deserialize(ref JsonReader reader, IJsonFormatterRe
 			while (reader.ReadIsInObject(ref count))
 			{
 				var property = reader.ReadPropertyNameSegmentRaw();
-				if (DictionaryResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
+				if (ResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
 				{
 					switch (errorValue)
 					{

src/Nest/XPack/Ssl/GetCertificates/GetCertificatesResponse.cs

@@ -1,11 +1,14 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.Serialization;
+using Elasticsearch.Net;
 
 namespace Nest
 {
+	[JsonFormatter(typeof(GetCertificatesResponseFormatter))]
 	public class GetCertificatesResponse : ResponseBase
 	{
+		[IgnoreDataMember]
 		public IReadOnlyCollection<ClusterCertificateInformation> Certificates { get; internal set; } =
 			EmptyReadOnly<ClusterCertificateInformation>.Collection;
 	}
@@ -34,4 +37,60 @@ public class ClusterCertificateInformation
 		[DataMember(Name = "expiry")]
 		public DateTimeOffset Expiry { get; internal set; }
 	}
+
+	internal class GetCertificatesResponseFormatter : IJsonFormatter<GetCertificatesResponse>
+	{
+		private static readonly ReadOnlyCollectionFormatter<ClusterCertificateInformation> Formatter =
+			new ReadOnlyCollectionFormatter<ClusterCertificateInformation>();
+
+		public void Serialize(ref JsonWriter writer, GetCertificatesResponse value, IJsonFormatterResolver formatterResolver) =>
+			throw new NotImplementedException();
+
+		public GetCertificatesResponse Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
+		{
+			var response = new GetCertificatesResponse();
+
+			if (reader.ReadIsNull())
+				return response;
+
+			switch (reader.GetCurrentJsonToken())
+			{
+				case JsonToken.BeginArray:
+					response.Certificates = Formatter.Deserialize(ref reader, formatterResolver);
+					break;
+				case JsonToken.BeginObject:
+					var count = 0;
+					while (reader.ReadIsInObject(ref count))
+					{
+						var property = reader.ReadPropertyNameSegmentRaw();
+						if (ResponseFormatterHelpers.ServerErrorFields.TryGetValue(property, out var errorValue))
+						{
+							switch (errorValue)
+							{
+								case 0:
+									if (reader.GetCurrentJsonToken() == JsonToken.String)
+										response.Error = new Error { Reason = reader.ReadString() };
+									else
+									{
+										var formatter = formatterResolver.GetFormatter<Error>();
+										response.Error = formatter.Deserialize(ref reader, formatterResolver);
+									}
+									break;
+								case 1:
+									if (reader.GetCurrentJsonToken() == JsonToken.Number)
+										response.StatusCode = reader.ReadInt32();
+									else
+										reader.ReadNextBlock();
+									break;
+							}
+						}
+						else
+							reader.ReadNextBlock();
+					}
+					break;
+			}
+
+			return response;
+		}
+	}
 }