update istio-ingress installation name in helm install instructions

[dhawton]

Please provide a description for what this PR is for.

Mesh Config has a default of looking for istio-ingressgateway, which is the name elsewhere and by other methods for installation. This PR changes the installation instructions to match the name used elsewhere. For example: https://istio.io/latest/docs/setup/additional-setup/gateway/#deploying-a-gateway, https://istio.io/latest/docs/setup/install/istioctl/#check-whats-installed.

Fixes #13497

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[zirain]

FYI: https://github.com/istio/istio.io/pull/11762#pullrequestreview-1087913597

[dhawton]

FYI: #11762 (review)

His comment is directed at the namespace rather than installation name. The installation name is inconsistent in this doc vs another doc with helm installation (ie, https://istio.io/latest/docs/setup/additional-setup/gateway/#deploying-a-gateway). This change aligns the general install doc with your gateway doc change PR here: https://github.com/istio/istio.io/pull/11734.

[zirain]

@howardjohn ptal

[dhawton]

This was intentional. Using the same names across samples, IMO, is actively harmful. users should understand what fields link things up and set them to match when appropriate.

We should not rely on a demo world where we happened to name everything the same. It ends with users thinking istio: ingressgateway is some magic value, when really its a simple label selector. I have seen this countless times. I have never seen the same with Kubernetes Service -- but probably we would, if their docs always used hello: world in every sample and treated it as a bug if it wasn't that.

@howardjohn However the current documentation varies from the default value we specify in the meshConfig for ingressService, which is istio-ingressgateway (https://istio.io/latest/docs/reference/config/istio.mesh.v1alpha1/#MeshConfig). This makes it feel like a bug since a user could follow the documentation as-is, and not have a working Ingress controller without additional steps that are not documented in this page. For a new person coming in to the project, installation steps are a great way to get started and not always best practice. As far as the linked comment by @zirain, I agree, the changing of namespaces is a good move and we document that in the Deploying Gateway docs.

I guess an alternative could be to update the documentation to clarify that the name in this step differs from meshConfig's default value and additional steps are required. I'm trying to approach this as someone who knows Kubernetes and Helm, but doesn't know Istio. I would follow the guide to get a learning environment setup and play in, and nothing seems to indicate that this wouldn't work "out of the box" until they go to test the environment and see the ingress not working.