Simplify validators

[jjngx]

Proposed changes

This PR simplify validation code. Business logic has not changed.

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

Merging #3818 (1b1264a) into main (1e92ba4) will decrease coverage by 0.46%.
The diff coverage is 98.57%.

@@            Coverage Diff             @@
##             main    #3818      +/-   ##
==========================================
- Coverage   52.40%   51.94%   -0.46%     
==========================================
  Files          59       59              
  Lines       16925    16759     -166     
==========================================
- Hits         8869     8705     -164     
+ Misses       7759     7756       -3     
- Partials      297      298       +1     

Impacted Files	Coverage Δ
pkg/apis/configuration/validation/policy.go	91.62% <95.83%> (+0.20%)	⬆️
...g/apis/configuration/validation/transportserver.go	96.37% <97.61%> (-0.44%)	⬇️
pkg/apis/configuration/validation/common.go	100.00% <100.00%> (ø)
...is/configuration/validation/globalconfiguration.go	87.27% <100.00%> (-1.07%)	⬇️
pkg/apis/configuration/validation/virtualserver.go	93.95% <100.00%> (-0.45%)	⬇️

... and 2 files with indirect coverage changes

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[lucacome]

Nice!