What would you like to be added:

Promote kube_statefulset_status_replicas_available, kube_statefulset_annotations, kube_statefulset_persistentvolumeclaim_retention_policy, and kube_statefulset_deletion_timestamp from EXPERIMENTAL to STABLE.
Update docs/metrics/workload/statefulset-metrics.md with descriptions, label details, and usage examples for these metrics.
Expand the StatefulSet PromQL and alerting examples to cover real-world monitoring scenarios.

Why is this needed:

These metrics already expose stable Kubernetes fields and haven’t changed since 2021. Marking them STABLE and documenting them removes confusion for users and gives teams ready-made queries and alerts for monitoring StatefulSets.

Describe the solution you’d like:

• Mark the four metrics as STABLE.
• Update docs/metrics/workload/statefulset-metrics.md with short descriptions, label details, and a few PromQL and alert examples.

Additional context