This is one way to allow access to all modules and file system from within jsreport.
new LocalReporting()
.UseBinary(JsReportBinary.GetBinary())
.Configure(cfg => cfg.AllowedLocalFilesAccess())
This allows just assets access
.Configure(cfg => {
cfg.AssetsConfiguration = new AssetsConfiguration() { AllowedFiles = "**/*.*" };
return cfg;
})