Don't crash with appsettings.json is missing, perhaps nicer message or create a default config.

[jafin]

If appsettings.json missing app throws exception

Unhandled exception. System.IO.FileNotFoundException: The configuration file 'appsettings.json' was not found and is not optional. The physical path is 'c:\Utils\CDE\appsettings.json'.
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.HandleException(ExceptionDispatchInfo info)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load()
   at Microsoft.Extensions.Configuration.ConfigurationRoot..ctor(IList`1 providers)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
   at cde.Config.ConfigBuilder.Build(String[] args)
   at cde.AppContainerBuilder.BuildContainer(String[] args)
   at cde.Program.InitProgram(String[] args)
   at cde.Program.Main(String[] args)