Use ETag to improve performance of issue notes polling
What does this MR do?
It avoids calls to the database when we poll for issue notes by implementing the proposal in https://gitlab.com/gitlab-org/gitlab-ce/issues/26926.
Are there points in the code the reviewer needs to double check?
- regular expression in the middleware
- cache expiry time
Why was this MR needed?
Notes polling generates high load on GitLab.com
Does this MR meet the acceptance criteria?
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Changelog entry added [ ] Documentation created/updated[ ] API support added- Tests
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Added for this feature/bug -
All builds are passing
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Conform by the merge request performance guides -
Conform by the style guides -
Branch has no merge conflicts with master(if it does - rebase it please) -
Squashed related commits together