feat: add ingressClassName value to ingress

[fkoetzner]

What issues does your PR fix?

• resolves allow users to set ingressClassName #427
• fixes Ingress Class Name reqired since k8s 1.19 #425
• replaces feat: allow users to set ingressClassName #426
• replaces feat: add ingressClassName to web/flower ingress #524

What does your PR do?

• Adds the following values to allow setting ingressClassName on the Ingress resources:
  • ingress.web.ingressClassName
  • ingress.flower.ingressClassName

Checklist

For all Pull Requests

• Commits are signed off
• Commits have semantic messages
• Documentation updated
• Passes ct linting

For releasing ONLY

• Chart.yaml version bumped
• CHANGELOG.md updated

---

P.S.: Sorry, I accidentally closed the original pull request #524.

[thesuperzapper]

@fkoetzner this looks good now, with only one random diff to be fixed.

Also, you can re-open closed PRs, you don't have to make new ones, otherwise, it's sort of spammy.

[thesuperzapper]

@fkoetzner I just realised that we haven't added ingressClassName to the v1beta1 versions of the Ingresses:

• ./templates/webserver/webserver-ingress-v1beta1.yaml
• ./templates/flower/flower-ingress-v1beta1.yaml

Can you clarify if v1beta1 ingresses have the ingressClassName field (as of Kubernetes 1.18+)?

• If YES, then we need to also include the value in those files
• If NO, then we should add a new validation to _helpers/validate-values.tpl that fails if ingress.apiVersion is networking.k8s.io/v1beta1 AND either ingressClassName is non-empty.

[fkoetzner]

@fkoetzner I just realised that we haven't added ingressClassName to the v1beta1 versions of the Ingresses:

* [./templates/webserver/webserver-ingress-v1beta1.yaml](https://github.com/airflow-helm/charts/blob/main/charts/airflow/templates/webserver/webserver-ingress-v1beta1.yaml)

* [./templates/flower/flower-ingress-v1beta1.yaml](https://github.com/airflow-helm/charts/blob/main/charts/airflow/templates/flower/flower-ingress-v1beta1.yaml)

Can you clarify if v1beta1 ingresses have the ingressClassName field (as of Kubernetes 1.18+)?

* If YES, then we need to also include the value in those files

* If NO, then we should  add a new validation to [_helpers/validate-values.tpl](https://github.com/airflow-helm/charts/blob/df99a33e3278de9f6935e747e8317794966ed979/charts/airflow/templates/_helpers/validate-values.tpl#L94-L95) that fails if `ingress.apiVersion` is `networking.k8s.io/v1beta1` AND either `ingressClassName` is non-empty.

Yes, you're right. I thought it was only added to networking.k8s.io/v1, but I tested it with v1beta1 and it works. Also, this confirms that v1beta1 has this field.