Helm chart support for periodic API server rollout restarts on Kubernetes

### Body

- depends on: #60940
- detail context in: https://github.com/apache/airflow/pull/60940#discussion_r2753284864

The new ‎`gunicorn` server type provides rolling worker restarts, but for users who continue to use the default ‎`uvicorn` mode on Kubernetes, it’s useful to have a first‑class mechanism in the Helm chart to periodically restart the API server pods.

This gives users an out‑of‑the‑box, supported way to manage long‑running API server processes when deploying Airflow to Kubernetes via the Helm chart.

We should enhance the official Airflow Helm chart to:

- Add an optional Kubernetes ‎`CronJob` (or equivalent mechanism) that:
- Periodically runs ‎`kubectl rollout restart deployment/airflow-api-server` (or the appropriate resource name).
- Has configurable schedule (cron expression), target deployment name, and enabled/disabled flag.

### Committer

- [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.