[Feature] Control plane load/usage metrics outside of Managed Prometheus

[pavneeta]

Is your feature request related to a problem? Please describe.
User to monitor the usage of APi-server and ETCD to understand how close to their control plane limits they are; currently these metrics are not available, and other metrics in Azure Monitor - Managed Prometheus are paid.

Describe the solution you'd like
See the APi-server and etcD CPU/Mem utilization metrics in Azure Monitor Platform metrics for AKS for free, so that I can alert on it.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

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Name	Display Name	Display Description
apiserver_memory_usage_percentage	API Server (PREVIEW) Memory Usage Percentage	Maximum memory percentage (based off current limit) used by API server pod across instances
apiserver_cpu_usage_percentage	API Server (PREVIEW) Cpu Usage Percentage	Maximum CPU  percentage (based off current limit) used by API server pod across instances
etcd_memory_usage_percentage	ETCD (PREVIEW) Memory Usage Percentage	Maximum memory percentage (based off current limit) used by ETCD pod across instances
etcd_cpu_usage_percentage	ETCD (PREVIEW) Cpu Usage Percentage	Maximum ETCD percentage (based off current limit) used by ETCD pod across instances
etcd_database_usage_percentage	ETCD (PREVIEW) Database Usage Percentage	Maximum  utilization of the ETCD database across instances

[julia-yin]

Update on 2/24:
Rollout of the new control plane platform metrics can be expected within the next few weeks.