Add GetNumProc util helper

[aobolensk]

• add GetNumProc helper to util library
• test GetNumProc
• document new helper in env variables guide

[github-actions]

Coverage report is available for download
here

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.78%. Comparing base (16d6e7a) to head (1dd00ca).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #533      +/-   ##
==========================================
+ Coverage   94.72%   94.78%   +0.05%     
==========================================
  Files          11       11              
  Lines         360      364       +4     
  Branches      122      124       +2     
==========================================
+ Hits          341      345       +4     
  Misses          5        5              
  Partials       14       14              

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