Set the `Access-Control-Expose-Headers` header to allow access to X-Error-Code in the browser
Since the dataset viewer on the Hub lets us navigate in the pages of rows, and search, all in the browser, we need to let the browser code access the X-Error-Code header, to be able to handle the errors adequately.

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers
Set the `Access-Control-Expose-Headers` header to allow access to X-Error-Code in the browser: Since the dataset viewer on the Hub lets us navigate in the pages of rows, and search, all in the browser, we need to let the browser code access the X-Error-Code header, to be able to handle the errors adequately.

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers