allow to define options in the plugin options

[FezVrasta]

 {
      plugin: CracoWorkboxPlugin,
      options: {
         GenerateSW: options => {
	       // override GenerateSW config here
	       // e.g. options.skipWaiting = true;
	       return options;
	     },
	     InjectManifest: options => {
	       // override InjectManifest config here
	       // e.g. options.maximumFileSizeToCacheInBytes = 10 * 1024 * 1024;
	       return options;
	     }
      },
    },
}