Publishing: Google Apps Script should detect changes to index in non-recent pages, too

[dominique-pfister]

The Google Apps Script currently checks once per hour, whether there was a change in the first 256 articles, by comparing the cached und uncached index for those. This will not work for older articles, though, as exemplified by this Slack discussion:

@rofe and @uncled I am aware of the updating on the hour. But I made this update a few hours ago (around noon ET) and I am still not seeing these two articles on the category page: https://blog.adobe.com/en/topics/outlook-2021.html

One conceivable approach in solving this problem is to return the last modified date of the document in the metadata section of the JSON or in a response header from content-proxy and compare it to the cached one.

[dominique-pfister]

Done, the purge script now not only checks the first index page for differences but also the Last-Modified date in the cached and uncached responses.