Use pagination without COUNT for issues/MRs
What does this MR do?
This changes the pagination system of MR and issue index pages so they don't use COUNT(*) queries, at the cost of not displaying page numbers. This saves around 30 milliseconds per page on GitLab.com. Since the page numbers aren't that useful this is an easy performance win.
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
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Changelog entry added, if necessary - Review
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Has been reviewed by UX -
Has been reviewed by Frontend -
Has been reviewed by Backend -
Has been reviewed by Database
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Conform by the merge request performance guides -
Conform by the style guides -
Squashed related commits together