Warn about Kerberos init container removal in Chart 1.2x

[aaron-y-chen]

related: #72555

Add deprecation warnings to the Chart 1.2x line for kerberosInitContainer settings that will be removed in Chart 2.0.

The warnings direct users to migrate legacy, Celery, Kubernetes, and Celery Worker Set configurations to the corresponding kerberosSidecar settings with startupProbe enabled.

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