Create -enable-oidc command line argument for OIDC policy

[haywoodsh]

Proposed changes

Create the -enable-oidc flag command line argument for the OIDC policy and deprecate the -enable-preview-policies flag.

• The OIDC policy requires -enable-oidc or -enable-preview-policies
• If -enable-preview-policies is used, returns a warning message about the deprecated flag but OIDC will still be valid.

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-commenter]

Codecov Report

Merging #2580 (cbba097) into main (192c76f) will decrease coverage by 0.10%.
The diff coverage is 38.88%.

❗ Current head cbba097 differs from pull request most recent head d883a06. Consider uploading reports for the commit d883a06 to get more accurate results

@@            Coverage Diff             @@
##             main    #2580      +/-   ##
==========================================
- Coverage   53.53%   53.43%   -0.11%     
==========================================
  Files          52       49       -3     
  Lines       14691    14304     -387     
==========================================
- Hits         7865     7643     -222     
+ Misses       6568     6418     -150     
+ Partials      258      243      -15     

Impacted Files	Coverage Δ
cmd/nginx-ingress/main.go	6.93% <0.00%> (+0.01%)	⬆️
internal/configs/config_params.go	76.74% <ø> (ø)
internal/configs/version1/config.go	0.00% <ø> (ø)
internal/k8s/controller.go	10.90% <20.00%> (+0.03%)	⬆️
internal/configs/configmaps.go	18.22% <100.00%> (ø)
pkg/apis/configuration/validation/policy.go	94.42% <100.00%> (-2.13%)	⬇️
internal/certmanager/helper.go
internal/certmanager/sync.go
... and 4 more

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[pleshakov]

Looks good! I left a few docs-related suggestion to make it consistent with the existing documentation.