front-proxy Ingress: add ingressClassName field

[ErwanDL]

The kubernetes.io/ingress.class annotation is deprecated since Kubernetes v1.18 (https://kubernetes.io/blog/2020/04/02/improvements-to-the-ingress-api-in-kubernetes-1.18/#deprecating-the-ingress-class-annotation).

This allows specifying an ingress class via the spec.ingressClassName field of the Ingress resource, and exposes a corresponding kcpFrontProxy.ingress.ingressClassName key in values.yaml.

Note: this should still be fully backwards-compatible. Users that for any reason still want to use the kubernetes.io/ingress.class annotation can always leave ingressClassName empty and rely on kcpFrontProxy.ingress.annotations just like before.

[kcp-ci-bot]

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[kcp-ci-bot]

Hi @ErwanDL. Thanks for your PR.

I'm waiting for a kcp-dev member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[sttts]

/ok-to-test

Sgtm

@mjudeikis looks good?