Need extensibility point for updating appsettings.json like we do for web.config in Intent Modules

[dandrejvv]

For Templates that wish to update the Web.config file in a Visual Studio project, they only need to register a decorator that inherits IXmlDecorator indirectly which gives the decorator access to the XDocument object to manipulate the XML DOM. This is the .NET Framework way of updating configuration files but there isn't anything yet for updating .NET Core configuration files appsettings.json. Perhaps one could have a IJsonDecorator that exposes some Json.Net object that allows one to easily query and manipulate the JSON DOM.