Resolve "Some Resources' Namespace is Hardcoded"

General MR

Summary

This MR updates resources declared in the istio-gateway package to use the .Release.Namespace template value instead of the hardcoded istio-gateway namespace name.

Relevant logs/screenshots

❯ kubectl get gateways -n istio-gateway
NAME                         AGE
passthrough-ingressgateway   17s
public-ingressgateway        17s

Linked Issue

#54 (closed)

Upgrade Notices

N/A