Add max-download-parallelism validation

[kislaykishore]

Reject 0 max-download-parallelism when parallel downloads enabled

Description

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

All modified and coverable lines are covered by tests ✅

Project coverage is 71.44%. Comparing base (52b1e10) to head (78cde58).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2046      +/-   ##
==========================================
- Coverage   71.46%   71.44%   -0.03%     
==========================================
  Files          99       99              
  Lines       10800    10802       +2     
==========================================
- Hits         7718     7717       -1     
- Misses       2735     2737       +2     
- Partials      347      348       +1     

Flag	Coverage Δ
unittests	71.44% <100.00%> (-0.03%)	⬇️

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