Update gateway injection doc

From James Force:

FYI - I've just tested gateway injection on 2.2.3 and this is my notes for setting up the ingress gateway (tested book info and all working good) https://github.com/james-cccc/ossm-productionisation-considerations/blob/main/defaultmesh/applications/vs2/01_vs2_gateways.yaml should the service we document be a type ClusterIP instead of a type LoadBalancer? Also probably worth documenting you need to create a network policy too?

Also, should we go one step beyond the current istio docs, as they state:

"This example shows the bare minimum needed to get a gateway running. For production usage, additional configuration such as HorizontalPodAutoscaler, PodDisruptionBudget, and resource requests/limits are recommended. These are automatically included when using the other gateway installation methods." - https://istio.io/latest/docs/setup/additional-setup/gateway/#deploying-a-gateway

Surely it'd be better for our customers to document a more fuller and production like example - happy to help on this

Text taken from comments in OSSMDOC-702