Removes control-plane affinity from Prometheus

[JosephSalisbury]

Towards https://github.com/giantswarm/giantswarm/issues/30772

Control plane nodes have the NoSchedule taint, which the Prometheus pods do not tolerate, so this affinity was unnecessary, and caused issues with Karpenter, e.g:

{"level":"DEBUG","time":"2024-05-21T11:12:03.942Z","logger":"controller.provisioner","message":"ignoring pod, label node-role.kubernetes.io/control-plane is restricted; specify a well known label: [karpenter.k8s.aws/instance-accelerator-count karpenter.k8s.aws/instance-accelerator-manufacturer karpenter.k8s.aws/instance-accelerator-name karpenter.k8s.aws/instance-category karpenter.k8s.aws/instance-cpu karpenter.k8s.aws/instance-encryption-in-transit-supported karpenter.k8s.aws/instance-family karpenter.k8s.aws/instance-generation karpenter.k8s.aws/instance-gpu-count karpenter.k8s.aws/instance-gpu-manufacturer karpenter.k8s.aws/instance-gpu-memory karpenter.k8s.aws/instance-gpu-name karpenter.k8s.aws/instance-hypervisor karpenter.k8s.aws/instance-local-nvme karpenter.k8s.aws/instance-memory karpenter.k8s.aws/instance-network-bandwidth karpenter.k8s.aws/instance-pods karpenter.k8s.aws/instance-size karpenter.sh/capacity-type karpenter.sh/provisioner-name kubernetes.io/arch kubernetes.io/os node.kubernetes.io/instance-type node.kubernetes.io/windows-build topology.kubernetes.io/region topology.kubernetes.io/zone], or a custom label that does not use a restricted domain: [k8s.io karpenter.k8s.aws karpenter.sh kubernetes.io]","commit":"34d50bf-dirty","pod":"golem-prometheus/prometheus-golem-0"}

Checklist

I have:

• [x] Described why this change is being introduced
• [x] Separated out refactoring/reformatting in a dedicated PR
• [x] Updated changelog in CHANGELOG.md

[JosephSalisbury]

oh yeah tests lol

[QuentinBisson]

go tests ./... -update should be fine :)