Added new JsonFields type

Author: t-vvidyasaga

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/SnapshotReference/JsonFields.cs

@@ -0,0 +1,10 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.SnapshotReference
+{
+    internal static class JsonFields
+    {
+        public const string SnapshotName = "snapshot_name";
+    }
+}