This commit adds the kube_*_deletion_timestamp metric for several Kubernetes resources:
- Deployments
- DaemonSets
- StatefulSets
- Services
- PodDisruptionBudgets
The deletion timestamp metric reports the Unix timestamp when a resource
was marked for deletion. This helps with monitoring resource lifecycle
and cleanup processes.
All metrics follow the same pattern:
- Help text: 'Unix deletion timestamp'
- Type: gauge
- Value: Unix timestamp in seconds when DeletionTimestamp is set,
otherwise the metric is not emitted
Updated documentation and tests are included for all affected resources.