What would you like to be added:

Add a timestamp metric when a Pod moves into the Unschedulable status, e.g., kube_pod_status_unscheduled_time.

Why is this needed:

In our operational use case, we need to display the duration of time a Pod has been in an unschedulable status within the Kubernetes console. This visibility is critical for troubleshooting scheduling failures and monitoring cluster health.

Describe the solution you'd like

Introduce a new metric similar to kube_pod_status_unscheduled_time to capture the exact timestamp when a Pod enters the Unschedulable phase. This metric should be exposed through kube-state-metrics to enable integration with existing monitoring systems.

Additional context

None