[Feature] Add nodepool-specific metrics for Cluster Autoscaler

**Is your feature request related to a problem? Please describe.**
While troubleshooting some CAS issues, a customer who uses Azure Managed Prometheus noticed that the following metrics seem to be missing:
```
cluster_autoscaler_node_group_backoff_status
cluster_autoscaler_node_group_healthiness
```

They see these in the CAS source code for the version which should be present with AKS & k8s 1.33, and are able to access other metrics such as `cluster_autoscaler_nodes_count`.

**Describe the solution you'd like**
AKS autoscale engineers have determined that these two metrics were not showing up because we do not set a flag on our managed deployment:
```
emitPerNodeGroupMetrics = flag.Bool("emit-per-nodegroup-metrics", false, "If true, emit per node group metrics.")
```
* code ref for where this is used + which metrics are impacted: [https://github.com/kubernetes/autoscaler/blob/9952269641c8cb71f197e61bc3e74eb9582d572f/cluster-auto…](https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fkubernetes%2Fautoscaler%2Fblob%2F9952269641c8cb71f197e61bc3e74eb9582d572f%2Fcluster-autoscaler%2Fmetrics%2Fmetrics.go%23L467-L474&data=05%7C02%7Crgregory%40microsoft.com%7C6d041392cc0e40159f5d08de3dcc7b4f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C639016145964963798%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=BYffTQUwMg4dNYNkr0kP5xjofQbJIqZ6PY%2FjsKr42k0%3D&reserved=0)

**Additional context**
This feature request is currently in our backlog. Please upvote this is you would like us to prioritize this workstream. Thanks.