Resolve "Configure and validate that Gateway pulls images from registry1"

General MR

Summary

• Removed the Gateway ImagePullSecret value in chart/values.yaml. The ImagePullSecret, image registry, and image tags are are now handled globally within the the Istiod chart values.yaml

Relevant logs/screenshots

Global values were validated in a test k3d cluster.

Linked Issue

#5 (closed)

Upgrade Notices

N/A

Closes #5 (closed)