Passthrough refactor

General MR

Summary

This MR converts the istiod chart to the passthrough pattern.

Relevant logs/screenshots

A test evidence MR exists in BB umbrella which shows this refactor passes BB umbrella pipeline smoke tests:

big-bang/bigbang!6096 (closed)

Linked Issue

big-bang/product/packages/istio-core#38

Upgrade Notices

N/A