Update deprecated annotations in example demo

[JoeyC-Dev]

Provide a description of what has been changed

The old annotation is being deprecated, and there will be a warning popped up for that.

helm install xkcd ./http-add-on/examples/xkcd 
fatal: destination path 'http-add-on' already exists and is not an empty directory.
W0418 05:55:35.571507    5828 warnings.go:70] annotation "kubernetes.io/ingress.class" is deprecated, please use 'spec.ingressClassName' instead

Checklist

• Commits are signed with Developer Certificate of Origin (DCO)
• Changelog has been updated and is aligned with our changelog requirements
• Any necessary documentation is added, such as:
  • README.md
  • The docs/ directory
  • The docs repo

Fixes #
Replace the annotation with current format, as indicated in: https://kubernetes.github.io/ingress-nginx/user-guide/basic-usage/

Test #
Works fine with the deployment of AKS.

# Create AKS
rG=joey-aks-keda-21612
aks=joey-aks-keda-21612

az group create -n ${rG} -l eastus 

az aks create -n ${aks} -g ${rG} --no-ssh-key --enable-keda --node-count 2 --node-vm-size Standard_A4_v2
az aks get-credentials -n ${aks} -g ${rG} 

# Install ingress-nginx
helm repo add ingress-nginx https://kubernetes.github.io/ingress-nginx
helm repo update

helm install ingress-nginx ingress-nginx/ingress-nginx \
  --create-namespace \
  --namespace ingress-basic \
  --set controller.service.annotations."service\.beta\.kubernetes\.io/azure-load-balancer-health-probe-request-path"=/healthz \
  --set controller.service.externalTrafficPolicy=Local

# Install keda http add-on
helm repo add kedacore https://kedacore.github.io/charts
helm repo update
helm install http-add-on kedacore/keda-add-ons-http --namespace kube-system

# Install example application with HTTPScaleObject
git clone -b patch-1 https://github.com/JoeyC-Dev/http-add-on.git
helm install xkcd ./http-add-on/examples/xkcd 

# Patch svc externalName
kubectl patch svc xkcd-proxy -p '{"spec":{"externalName": "keda-add-ons-http-interceptor-proxy.kube-system"}}'

# Get Ingress IP
sleep 30; ip=$(kubectl get ingress xkcd -o=jsonpath='{.status.loadBalancer.ingress[0].ip}')

# Test request
curl -H "Host: myhost.com" ${ip}/path1

# Clean up the resource
az group delete -n ${rG} --no-wait

[JorTurFer]

Thanks for the improvement! ❤️

[JoeyC-Dev]

@JorTurFer Thank you for the reviewing, but the check is failed due to incorrect order in changelog.
https://github.com/kedacore/http-add-on/actions/runs/8733241431/job/23962464570?pr=979

Can you set auto-merge for this PR again? Thanks.

[JorTurFer]

Can you set auto-merge for this PR again? Thanks.

Sure!