Implement path dependent feed_token

What does this MR do and why?

Implement Defense in depth: path dependent feed token (#414257 - closed) to add per-path feed/calendar token.

How to set up and validate locally

1. go to any issues list and click the Subscribe to RSS feed / Subscribe to calendar links
2. Observe the feed_token parameter in the form glft-64CHARHEXSTRING-CURRENTUSERID

This type of feed_token will only work for the URL it was generated for. So user/project1/-/issues.atom will have a different feed_token than user/project2/-/issues.atom or user/project1/-/merge_requests.atom.

The feed token under /-/profile/personal_access_tokens will still work for any RSS/ics feed and it also can be used to generate the per-path token.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.