feat: Secret references in NGINX Ingress controller annotations support

[dabico]

What this PR does / why we need it?

Take values of specific nginx.ingress.kubernetes.io annotations into consideration when performing scans of Secret resources referenced in Ingress.

PR Checklist

• This PR adds K8s exceptions (false positives)
• This PR adds new code
• This PR includes tests for new/existing code
• This PR adds docs

GitHub Issue

Closes #560

Notes for your reviewers

The current approach has a limitation: it only takes into account secret references within the same namespace. The NGINX ingress controller annotations can actually reference secrets from other namespaces. Not sure how to implement this cleanly cleanly in the current approach, while taking flags like --exclude-namespace into consideration.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 53.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.69%. Comparing base (63151f6) to head (4eb4019).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/kor/secrets.go	53.33%	6 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #564      +/-   ##
==========================================
- Coverage   45.74%   45.69%   -0.06%     
==========================================
  Files          69       69              
  Lines        3941     3950       +9     
==========================================
+ Hits         1803     1805       +2     
- Misses       1838     1844       +6     
- Partials      300      301       +1     

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