refactor: reuse code moved in kyverno repo

[eddycharly]

This PR reuses some code moved in the kyverno repo and shared with the CLI

[codecov]

Codecov Report

Merging #498 (a4967ec) into main (c323703) will decrease coverage by 3.26%.
The diff coverage is 81.08%.

@@            Coverage Diff             @@
##             main     #498      +/-   ##
==========================================
- Coverage   19.48%   16.23%   -3.26%     
==========================================
  Files          12        9       -3     
  Lines         616      573      -43     
==========================================
- Hits          120       93      -27     
+ Misses        469      455      -14     
+ Partials       27       25       -2     

Files Changed	Coverage Δ
backend/pkg/server/api/engine/handler.go	36.48% <ø> (ø)
backend/pkg/policy/load.go	64.51% <76.92%> (ø)
backend/pkg/exception/load.go	83.33% <83.33%> (ø)
backend/pkg/server/api/engine/request.go	46.15% <83.33%> (ø)

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