Migrate ingress.class annotation to new IngressClassName field

[aledbf]

What this PR does / why we need it:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Which issue/s this PR fixes

How Has This Been Tested?

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[aledbf]

/retest

[codecov-io]

Codecov Report

Merging #5307 into master will increase coverage by 0.05%.
The diff coverage is 60.52%.

@@            Coverage Diff             @@
##           master    #5307      +/-   ##
==========================================
+ Coverage   58.64%   58.70%   +0.05%     
==========================================
  Files          88       88              
  Lines        6901     6908       +7     
==========================================
+ Hits         4047     4055       +8     
  Misses       2410     2410              
+ Partials      444      443       -1     

Impacted Files	Coverage Δ
cmd/nginx/main.go	6.41% <0.00%> (-0.09%)	⬇️
internal/k8s/main.go	69.23% <25.00%> (+3.77%)	⬆️
internal/ingress/status/status.go	70.98% <71.42%> (ø)
internal/ingress/annotations/class/main.go	88.88% <85.71%> (+17.46%)	⬆️
internal/ingress/controller/store/store.go	59.95% <88.88%> (+0.30%)	⬆️
cmd/nginx/flags.go	83.08% <100.00%> (ø)

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[aledbf]

/retest

[cmluciano]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, cmluciano

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• OWNERS [aledbf]

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[ElvinEfendi]

This log message is confusing, so we enable new ingress features in ingress V1 is NOT ready?

[janosi]

Hello @aledbf @cmluciano Maybe I misunderstand the code, but is it so that from now on the annotation is not taken into consideration?
I just ask this as I understand the API specification a bit different here: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.18/#ingressspec-v1beta1-networking-k8s-io
For backwards compatibility, when that annotation is set, it must be given precedence over this field.

[janosi]

OK, I can see now. the toIngress() function puts the annotation's value into the Spec if there is annotation. So, the annotation becomes "Spec.IngressClassName" before the isValid() is called.
Sorry for the mess.