Ensure all fields are taken into account with NPM

[CharlyF]

What does this PR do?

NPM options collectDNSStats and enableConntrackare not taken into account (converted as env vars), so we rely on the sys probe behavior, which will enable both if they are not configured. Unfortunately:

  features:
    npm:
      collectDNSStats: false
      enableConntrack: false
      enabled: true 

will result in both of them turned on.

Motivation

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Additional Notes

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[codecov-commenter]

Codecov Report

Merging #678 (864fad3) into main (114599e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #678      +/-   ##
==========================================
+ Coverage   58.54%   58.57%   +0.02%     
==========================================
  Files         144      144              
  Lines       17376    17387      +11     
==========================================
+ Hits        10173    10184      +11     
  Misses       6593     6593              
  Partials      610      610              

Flag	Coverage Δ
unittests	58.57% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
controllers/datadogagent/feature/npm/feature.go	91.53% <100.00%> (+0.78%)	⬆️

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