Implement limit on max-concurrency.

[kislaykishore]

Description

Limit max-concurrency of parallel downloads across jobs using a semaphore.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - NA

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.45%. Comparing base (3c70dc9) to head (2d7ca17).
Report is 3 commits behind head on master.

Files	Patch %	Lines
internal/cache/file/downloader/test_util.go	83.33%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2032      +/-   ##
==========================================
- Coverage   71.54%   71.45%   -0.09%     
==========================================
  Files          98       99       +1     
  Lines       10756    10805      +49     
==========================================
+ Hits         7695     7721      +26     
- Misses       2718     2736      +18     
- Partials      343      348       +5     

Flag	Coverage Δ
unittests	71.45% <90.00%> (-0.09%)	⬇️

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[sethiay]

Logic looks good, some comments on the tests.