Sets global values for registry, Image tag, and ImagePullSecret

General MR

Summary

• Set global values for the registry, image tag, and ImagePullSecret. Global values are used for Istiod and Gateway chart deployments.
• Removed the istiod chart specific values for registry, image tag, and ImagePullSecret.
• Added docs/DEVELOPMENT_MAINTENANCE to track chart value deviations from upstream.
• Added Ronald to CODEOWNERS.

Relevant logs/screenshots

Tested global values settings in k3d cluster for both Istiod and Gateway packages.

Linked Issue

Gateway Issue #5

Upgrade Notices

N/A