Add startup probe for Kerberos worker sidecars

[aaron-y-chen]

related: #35154

Summary

Add a configurable klist -s startup probe to Kerberos worker sidecars as a prerequisite for adopting native Kubernetes sidecars.

File	Purpose and design principle
chart/values.yaml	Defines default-enabled probe settings for Celery and Kubernetes workers. The approximately 60-second failure window allows time to obtain the initial Kerberos credentials.
chart/values.schema.json	Validates the new settings and intentionally exposes only enablement and timing controls. The probe type and command remain fixed to preserve its Kerberos-specific semantics.
chart/templates/workers/worker-deployment.yaml	Renders the klist -s exec probe for the Celery worker Kerberos sidecar. Users of custom images without klist can disable it.
chart/files/pod-template-file.kubernetes-helm-yaml	Applies the same probe contract to the KubernetesExecutor worker pod template.
chart/tests/helm_tests/security/test_kerberos.py	Verifies the Celery worker probe's default, customized, and disabled rendering.
chart/tests/helm_tests/airflow_aux/test_pod_template_file.py	Verifies the same three cases for the KubernetesExecutor pod template.

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