Add a new private kubernetes cluster in the new sponsored azure subscription

[smerle33]

Service(s)

Azure, infra.ci.jenkins.io, release.ci.jenkins.io

Summary

as per #3918 (comment)

• "Using subscription credits instead of CDF money" followinghttps://github.com/ [Sponsorships] Setup the secondary Azure subscription to consume the sponsor credits #3818 and Migrate ci.jenkins.io to the sponsored subscription #3913
• "Continue work about infra.ci on arm64" as part of infra.ci.jenkins.io on arm64 (controller and agents) #3823

=> Let's scope the initial implementation to only infra.ci.jenkins.io agents, and only 1 "non system" nodepool of type linux/arm64 so we can start switching workloads out of privatek8s.

add a new AKS cluster only for infra.ci.jenkins.io and release.ci.jenkins.io Kubernetes agents

• Create a new AKS cluster privatek8s-sponsored
  • Managed in jenkins-infra/azure with Terraform
  • Same settings as the current [privatek8s] (https://github.com/jenkins-infra/azure/blob/0cf6c87851af116dc6b7ec955683753db8b47ce5/privatek8s.tf#L24) but with only nodepools for agents
  • set network to manage bridge between the current privatek8s cluster and this one
• add this cluster to kubernetes-management
  • Creates a service-account with token + insert it in infra.ci secrets
  • Add initial "foundation" services (private + public ingress, cert-manager, datadog, falco)

Reproduction steps

No response