Improve performance of show.json action (rendered) for Projects::BlobController under load into the s4 tier

Create team has made a great improvement to the Projects::BlobController#show.json controller and action, it went down from 2.2s to under 1.2s for rendered files (files that are shown with the viewer=rich param, e.g. markdown files):

█ Results summary
* Environment:                10k
* Environment Version:        14.0.0-pre `c6e57e5aa5c`
* Option:                     60s_200rps
* Date:                       2021-06-02
* Run Time:                   1h 27m 8.43s (Start: 04:35:44 UTC, End: 06:02:52 UTC)
* GPT Version:                v2.8.0

NAME                       | RPS   | RPS RESULT           | TTFB AVG  | TTFB P90              | REQ STATUS     | RESULT 
---------------------------|-------|----------------------|-----------|-----------------------|----------------|--------
web_project_file_rendered  | 20/s  | 15.83/s (>9.60/s)    | 892.91ms  | 1290.67ms (<3000ms)   | 100.00% (>99%) | Passed

 █ Web - Project File Rendered
     data_received.................................: 921 MB  15 MB/s
     data_sent.....................................: 133 kB  2.2 kB/s
     group_duration................................: avg=2333.02ms min=762.83ms med=1852.08ms max=12618.94ms p(90)=2754.09ms p(95)=3513.36ms
     http_req_blocked..............................: avg=0.08ms    min=0.00ms   med=0.01ms    max=5.78ms     p(90)=0.01ms    p(95)=0.03ms   
     http_req_connecting...........................: avg=0.06ms    min=0.00ms   med=0.00ms    max=2.12ms     p(90)=0.00ms    p(95)=0.00ms   
     http_req_duration.............................: avg=897.49ms  min=333.33ms med=671.49ms  max=12566.12ms p(90)=1291.74ms p(95)=1628.77ms
       { expected_response:true }..................: avg=897.49ms  min=333.33ms med=671.49ms  max=12566.12ms p(90)=1291.74ms p(95)=1628.77ms
     http_req_failed...............................: 0.00%   ✓ 0    ✗ 962 
     http_req_receiving............................: avg=4.53ms    min=0.47ms   med=4.43ms    max=26.75ms    p(90)=8.61ms    p(95)=10.39ms  
     http_req_sending..............................: avg=0.04ms    min=0.02ms   med=0.04ms    max=0.16ms     p(90)=0.06ms    p(95)=0.08ms   
     http_req_tls_handshaking......................: avg=0.00ms    min=0.00ms   med=0.00ms    max=0.00ms     p(90)=0.00ms    p(95)=0.00ms   
     http_req_waiting..............................: avg=892.91ms  min=331.95ms med=664.67ms  max=12549.34ms p(90)=1290.67ms p(95)=1605.97ms
     ✓ { endpoint:file?format=json&viewer=rich }...: avg=1337.58ms min=630.18ms med=723.83ms  max=12549.34ms p(90)=1605.87ms p(95)=2415.08ms
     ✓ { endpoint:file }...........................: avg=448.25ms  min=331.95ms med=372.92ms  max=3527.27ms  p(90)=575.70ms  p(95)=672.74ms 
   ✓ http_reqs.....................................: 962     15.831609/s
     ✓ { endpoint:file?format=json&viewer=rich }...: 481     7.915804/s
     ✓ { endpoint:file }...........................: 481     7.915804/s
     iteration_duration............................: avg=2328.20ms min=0.14ms   med=1851.70ms max=12619.02ms p(90)=2753.71ms p(95)=3511.30ms
     iterations....................................: 481     7.915804/s
   ✓ successful_requests...........................: 100.00% ✓ 962  ✗ 0   
     vus...........................................: 2       min=2  max=20
     vus_max.......................................: 20      min=20 max=20

The test was done against a "worse case" file, CHANGELOG.md, (~770kb).

As part of the performance targets this page now falls into the severity3 tier.

Task is to reduce the performance of this page to the next tier of severity4 (<1000ms).