Issue Detail - Frontend Performance Research Spike

We have a Q3 OKR in both Product and Dev to improve the LCP performance of the top 5 most visited routes on GitLab.com.

Because devopsplan is awesome, we have two of those top 5 most visited routes: the Issue List and the Issue Detail page.

This issue represents a research spike to identify actions that we can take on the backend for the Issue Detail to improve the performance of this page. We want to identify actions that we can take in %13.5 to improve frontend performance. We will likely spend a significant portion of %13.5 implementing these performance improvements.

Dashboard: https://dashboards.gitlab.net/d/000000043/sitespeed-page-summary?orgId=1&from=now-30d&to=now&var-base=sitespeed_io&var-path=desktop&var-group=gitlab_com&var-page=_gitlab-org_gitlab-foss_issues_34225&var-browser=chrome&var-connectivity=cable&var-function=median

Sitespeed report: https://storage.googleapis.com/sitespeed-results-gitlab/gitlab.com/2020-05-26-03-57-29/pages/gitlab.com/gitlab-org/gitlab-foss/issues/34225/index.html

Done when:

• We've identified 2-5 frontend performance optimizations for the Issue Detail page.
• Those optimizations are documented as issues and included in the epic

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I know that having a "Research spike" can be a bit nebulous in terms of what success is, and ultimately the goal here is to improve the overall performance of GitLab, so if there are other related issues that you're aware of that help push us towards this goal, feel free to include those here. For example, we're tracking #204720 (closed) to improve the performance of complex sorts on Issue List. That doesn't directly impact the Sitespeed report metrics, but would still be a big performance win.