fix(helm): apply global.imagePullSecrets to Envoy Proxy deployments

[blacksd]

What type of PR is this? Bug fix

What this PR does / why we need it: This PR fixes an issue where the global.imagePullSecrets configuration in the gateway-helm chart was not being applied to dynamically created Envoy Proxy deployments. While the global imagePullSecrets setting was correctly applied to the Envoy Gateway controller deployment and rate limit deployment, it was missing from the Envoy Proxy deployments that are created when Gateway resources are instantiated.

Background: The gateway-helm chart follows a consistent pattern where global configuration parameters (like global.imagePullSecrets and global.imageRegistry) are propagated to all component deployments:

• Envoy Gateway controller deployment: Uses global.imagePullSecrets or deployment.envoyGateway.imagePullSecrets or global.images.envoyGateway.pullSecrets
• Rate limit deployment: Uses global.imagePullSecrets or global.images.ratelimit.pullSecrets
• Envoy Proxy deployments (fixed by this PR): Now uses global.imagePullSecrets

Changes:

• Updated eg.default-envoy-gateway-config template to include envoyDeployment.pod.imagePullSecrets configuration
• This configuration is applied through the EnvoyGateway provider settings, which control how the Envoy Gateway controller creates Envoy Proxy deployments
• Added release note documenting the fix

Impact: Users deploying Envoy Gateway in environments with private container registries can now set global.imagePullSecrets once, and it will be correctly applied to all components including the dynamically created Envoy Proxy deployments. This ensures consistent behavior across all chart-managed resources.

Which issue(s) this PR fixes: Fixes #

Release Notes: Yes