test: add helm snapshot test for deployment extraEnv

Signed-off-by: Giri Kuncoro <girikuncoro@gmail.com>

Author: girikuncoro

test/helm/gateway-helm/deployment-extraenv.in.yaml

@@ -0,0 +1,13 @@
+global:
+  images:
+    envoyGateway:
+      image: "docker.io/envoyproxy/gateway-dev:latest"
+      pullPolicy: Always
+
+deployment:
+  envoyGateway:
+    extraEnv:
+    - name: OTEL_METRICS_EXEMPLAR_FILTER
+      value: always_off
+    - name: GOGC
+      value: "50"