Detect requests to pages that no longer exist and investigate link forwarding

[surchs]

We have changed our docs structure quite a bit, and we likely will continue in the future. If an old link points to a page we no longer have, the user sees a 404 page. It would be nice if we could get a log of the pages hit in this way, and maybe also where from. Then we could occasionally go and try to update the original link.

To prevent breaking links in other users/groups' own docs, we should also investigate link forwarding for high-traffic pages when we do restructure links.

[github-actions]

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