Improve browser Total Blocking Time (TBT) performance of Project File Blame page into S2 tier

Starting from 2021-11-01 GitLab version 14.5.0-pre - eea9ad536fa Project File Blame page's browser Total Blocking Time (TBT) performance has degraded significantly to 11073ms, the last successful run with TBT ~2600ms was on 14.5.0-pre - 45da3d6db76

• First failed job: https://gitlab.com/gitlab-org/quality/performance/-/wikis/Benchmarks/SiteSpeed/10k?version_id=de83914bd667e7080c0bb1c648c679cf8d881707
• Last succesful job: https://gitlab.com/gitlab-org/quality/performance/-/wikis/Benchmarks/SiteSpeed/10k?version_id=34bcf76210e873521ba72fe1ed8e4a5cb611e148
• GitLab changes between versions: 45da3d6d...eea9ad53

* Environment:                10k
* Environment Version:        14.5.0-pre `a9bae7b7a99`
* Date:                       2021-11-02
NAME                                  | FCP (ms) | LCP (ms)       | TBT (ms)        | SI (ms) | LVC (ms) | TFR SIZE (kb) | SCORE | RESULT
--------------------------------------|----------|----------------|-----------------|---------|----------|---------------|-------|-------
web_project_file_blame                | 3158     | ✓ 3303 (<5000) | ✘ 11525 (<4000) | 3557    | 19167    | 635.4         | 77    | FAILED

Results before 2021-11-01

After the amazing work that was done in #331445 (comment 642726015) the Project File Blame page's browser Total Blocking Time (TBT) performance got significantly improved and now it's slightly over the S2 target:

NAME                   | FCP (ms) | LCP (ms)        | TBT (ms)         | SI (ms) | LVC (ms) | TFR SIZE (kb) | SCORE | RESULT
-----------------------|----------|-----------------|------------------|---------|----------|---------------|-------|-------
web_project_file_blame | 3295     | ✓ 3447 (<5000)  | ✓ 2193 (<20000)  | 3612    | 10200    | 574.1         | 83    | Passed

The Project File Blame page being tested can be seen here on Staging. This page is showing blame results for the 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 over the target of 9000 ms which is severity1 . Task is to improve the page's browser performance into next tier.