Expand mgmt configmap tests

[nginx-bot]

Proposed changes

Add further tests to validate parameters passed to the mgmt configmap

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 9 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-4.0@0a5e471). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
internal/configs/configmaps.go	40.00%	4 Missing and 2 partials ⚠️
internal/validation/validation.go	86.36%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release-4.0    #7000   +/-   ##
==============================================
  Coverage               ?   52.74%           
==============================================
  Files                  ?       89           
  Lines                  ?    20824           
  Branches               ?        0           
==============================================
  Hits                   ?    10983           
  Misses                 ?     9387           
  Partials               ?      454           

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