A new header name, Etag: "<value>" is added in page response's header. So we are able to this page ETag
value to monitor if each page is changed or not by given a page link and page ETag.
Able to use page ETag value to monitor if a specific page has changed or not.
If the page changed, it will return status code 200, and the settings in the page.
If no change, status code 304(ResourceNotModifiedError) returned without settings. 304 should not be an exception but a successful call but no setting in return.