Ensure legacy hardened values works for istiod

When migrating to bb-common I did not create a legacy -> bb-common mapping of values for the istiod.hardened.enabled value, which results in a scenario where not setting istiod.hardened.enabled=false would effectively disable hardened mode for every package besides istiod.

The fix involves mapping the legacy istiod.values.hardened configuration to the appropriate bb-common configuration.