Document Istio installation options sidecar vs no sidecar

[tcnghia]

Describe the change you'd like to see
We need to clearly document our Istio installation in case of sidecar vs no sidecar setups. In the no sidecar setup, where the cluster-local-gateway is needed, we should convert to using the IstioOperator / Istio profile to be more aligned with other existing Istio users who will also be using IstioOperator as well.

cc @nak3 @ZhiminXiang

Additional context

[nak3]

/assign

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen.Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[nak3]

/reopen
/remove-lifecycle stale

[knative-prow-robot]

@nak3: Reopened this issue.

Details

In response to this:

/reopen
/remove-lifecycle stale

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[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen.Mark the issue as
fresh by adding the comment /remove-lifecycle stale.