Extended pagination for security advisory RSS feeds

I have been working on a system to track security advisories from the Core and Contrib RSS feeds on drupal.org, using them to monitor a range of Drupal sites and patch/upgrade them as appropriate. Unfortunately, the RSS feed as it currently stands only provides the most recent 50 items, rather than the full archive of advisories.

Adding pagination links to the existing RSS feed would allow systems to visit earlier pages and ingest a full set of advisories.

Increasing the 50-item limit is not an ideal solution, as it sacrifices performance for people who only want recent updates, and we may eventually run into the same problem with advisories starting to "drop off" the end of the feed in time.

Ideally adding a pagination parameter to the rss.xml URLs, and first/last/previous/next URLs as link elements, would enable easier machine-readable access to all of the advisories. Alternately, provide a separate rss-archive.xml link that retrieves a full set of advisories.

I am aware that there has been some discussion around moving security advisories to a standardised, verified content type. This feature request could be a good adjunct to improving machine-readable access to advisories.

The relevant standard for RSS paging and archiving is RFC 5005:
- https://tools.ietf.org/html/rfc5005