Refactor to prepare for structured logs

[AlexFenlon]

Proposed changes

refactor flags.go parseFlags to prepare for struct logs.

We are looking to split the flag parsing from the validation as we want to pass the logger to the validation function.

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 0% with 32 lines in your changes missing coverage. Please review.

Project coverage is 53.20%. Comparing base (f6afacb) to head (2d594ca).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/nginx-ingress/flags.go	0.00%	31 Missing ⚠️
cmd/nginx-ingress/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6501      +/-   ##
==========================================
- Coverage   53.25%   53.20%   -0.05%     
==========================================
  Files          85       85              
  Lines       16016    16018       +2     
==========================================
- Hits         8529     8523       -6     
- Misses       7081     7087       +6     
- Partials      406      408       +2     

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[jjngx]

🚀