fix opening of BuildJsonConfig model

Author: rmannibucau

src/Docfx.App/Config/FileMetadataPairs.cs

@@ -9,7 +9,7 @@ namespace Docfx;
 /// <see cref="BuildJsonConfig.FileMetadata"/>
 /// <see cref="MergeJsonItemConfig.FileMetadata"/>
 [Newtonsoft.Json.JsonConverter(typeof(FileMetadataPairsConverter))]
-internal class FileMetadataPairs
+public class FileMetadataPairs
 {
     // Order matters, the latter one overrides the former one
     private readonly List<FileMetadataPairsItem> _items;

src/Docfx.App/Config/FileMetadataPairsItem.cs

@@ -10,7 +10,7 @@ namespace Docfx;
 /// Glob/Value pair to define define file's metadata.
 /// </summary>
 /// <see cref="FileMetadataPairs"/>
-internal class FileMetadataPairsItem
+public class FileMetadataPairsItem
 {
     /// <summary>
     /// The glob pattern to match the files.

src/Docfx.App/Config/GroupConfig.cs

@@ -9,7 +9,7 @@ namespace Docfx;
 /// <summary>
 /// Group configuration.
 /// </summary>
-internal class GroupConfig
+public class GroupConfig
 {
     /// <summary>
     /// Defines the output folder of the generated build files.

src/Docfx.App/Config/ListWithStringFallback.cs

@@ -7,7 +7,7 @@ namespace Docfx;
 /// ListWithStringFallback.
 /// </summary>
 [Newtonsoft.Json.JsonConverter(typeof(ListWithStringFallbackConverter))]
-internal class ListWithStringFallback : List<string>
+public class ListWithStringFallback : List<string>
 {
     /// <summary>
     /// Initializes a new instance of the <see cref="ListWithStringFallback"/> class.