Support configuring envoyproxy infra attributes in the Helm chart

[Xunzhuo]

Description:

Describe the desired behavior, what scenario it enables and how it
would be used.

In vendor, it has some scenarios for configuring envoyproxies attributes. It would be nice to configure all the envoyproxy knobs in the helm chart.

[optional Relevant Links:]

Any extra documentation required to understand the issue.

[arkodg]

+1 to this, a envoyProxy / envoyProxyTemplate field could be added to

gateway/api/v1alpha1/envoygateway_types.go

Line 154 in 71c0b54

type Gateway struct {

This now introduces 3 levels of EnvoyProxy configuration (EnvoyGateway, EnvoyProxy attached to GatewayClass, EnvoyProxy attached to Gateway)
The current merge Strategy is Replace and most specific one wins, so if the admin set the image value at top level it will be overridden if any other value is set in the lower level EnvoyProxy (all fields are replaced today)

There is the Merge Strategy option tracked with #1934