Add parallel downloads job

[sethiay]

Description

Add parallel downloads job

Note: I will add more unit/composite tests in the next PR. Also, I will enable the configs to run e2e tests with parallel downloads in a separate PR.

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 90.15152% with 13 lines in your changes missing coverage. Please review.

Project coverage is 71.50%. Comparing base (b6eca68) to head (7d92738).

Files	Patch %	Lines
internal/cache/file/downloader/job.go	89.65%	7 Missing and 2 partials ⚠️
...al/cache/file/downloader/parallel_downloads_job.go	91.11%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2005      +/-   ##
==========================================
+ Coverage   71.40%   71.50%   +0.10%     
==========================================
  Files          97       98       +1     
  Lines       10708    10740      +32     
==========================================
+ Hits         7646     7680      +34     
+ Misses       2719     2717       -2     
  Partials      343      343              

Flag	Coverage Δ
unittests	71.50% <90.15%> (+0.10%)	⬆️

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[raj-prince]

A couple of minor comments.

[vadlakondaswetha]

Will rely on Prince review for unit tests

[raj-prince]

Few nits.

LGTM, assuming we are adding unit tests for newly added method as separate PR.