refactor: replace glog in flags.go

[pdabelf5]

Proposed changes

• remove google/glog from flags.go
• move log levels to their own package

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 7.14286% with 78 lines in your changes missing coverage. Please review.

Project coverage is 53.27%. Comparing base (3d3284f) to head (ba0dab6).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/nginx-ingress/flags.go	0.00%	77 Missing ⚠️
cmd/nginx-ingress/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6530      +/-   ##
==========================================
- Coverage   53.30%   53.27%   -0.04%     
==========================================
  Files          87       87              
  Lines       16074    16136      +62     
==========================================
+ Hits         8569     8596      +27     
- Misses       7097     7132      +35     
  Partials      408      408              

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