Improve browser Total Blocking Time (TBT) performance of Project File Rendered (Markdown) page to meet the target

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The Project File Rendered page's browser Total Blocking Time (TBT) performance is unperformant:

* Environment:                10k
* Environment Version:        16.4.0-pre `4cb1a0aba18`
* Date:                       2023-09-05
NAME                                  | FCP (ms) | LCP (ms)       | TBT (ms)       | SI (ms) | LVC (ms) | TFR SIZE (kb) | SCORE | RESULT
--------------------------------------|----------|----------------|----------------|---------|----------|---------------|-------|-------
web_project_file_rendered             | 1605     | ✓ 5219 (<7300) | ✓ 1193 (<2000) | 2850    | 8300     | 1691.6        | 72    | Passed

The Project File Rendered page being tested can be seen here on Staging. This page is showing rendered markdown file, below is the screenshot of page's historical test TBT results

Test Details

Testing was done on our 10k Reference Architecture environment with our lab condition SiteSpeed pipeline (named GitLab Browser Performance Tool internally). The project being tested is a copy of gitlabhq (tarball can be found here). GitLab Browser Performance Tool tests information is listed at Current test details page.

The latest GitLab Browser Performance pipeline results can always be found here. Through this page the full SiteSpeed report can be found via the SiteSpeed Report link on that page.

As per our performance targets this page's TBT metric is above the target of 1000 ms which is severity3 . Task is to improve the page's browser performance to meet the target.