Istio Compat: Support Sidecar Injection on Gateway Proxies for Revision Istio

[bgottfried91]

Gloo Edge Version

1.12.x (beta)

Kubernetes Version

1.23.x

Describe the bug

The new Helm value global.istioIntegration.enableIstioSidecarOnGateway that should apply a label to any gatewayProxies created during Edge install currently only applies the istio-injection: enabled label. This label, when applied to a Pod directly (as opposed to applied to a namespace), will only work for Istio installations that are not using revisions. For revisioned Istio, you must use the label istio.io/rev: <revision>.

Steps to reproduce the bug

1. Install Istio with revisions
2. Install Gloo Edge with the global.istioIntegration.enableIstioSidecarOnGateway value set to true.
3. Confirm that the gateway proxy/proxies does/do not have sidecars injected

Expected Behavior

When using that Helm value, it should inject sidecars whether Istio is revisioned or not.

Additional Context

I'd think we could fix this pretty quickly just by changing the chart behavior so that if another value exists, like global.istioIntegration.enableIstioSidecarOnGateway.revision, the chart instead generates the istio.io/rev label instead of istio-injection label.