Add websocket session message type to generated openapi.json

Jellyfin.Server/Filters/WebsocketModelFilter.cs

@@ -25,6 +25,8 @@ namespace Jellyfin.Server.Filters
             context.SchemaGenerator.GenerateSchema(typeof(GeneralCommandType), context.SchemaRepository);
 
             context.SchemaGenerator.GenerateSchema(typeof(GroupUpdate<object>), context.SchemaRepository);
+
+            context.SchemaGenerator.GenerateSchema(typeof(SessionMessageType), context.SchemaRepository);
         }
     }
 }