Add helm installation steps for multi-cluster

[nshankar13]

Description

Adds Helm multi-cluster installation steps for all Istio multi-cluster control plane models and network topologies.

Preview link for quick reference: https://deploy-preview-15459--preliminary-istio.netlify.app/latest/docs/setup/install/multicluster/multi-primary/

Resolves: #14765

Tested against Istio 1.23.0-alpha.0 Helm charts.

Reviewers

• Ambient
• Docs
• Installation
• Networking
• Performance and Scalability
• Extensions and Telemetry
• Security
• Test and Release
• User Experience
• Developer Infrastructure
• Localization/Translation

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[dhawton]

Since you're updating snips here, make sure they get added to the testing.

[nshankar13]

@dhawton any ideas on why the lint check is complaining about spelling here?

"Install Istio as primary in cluster1 using istioctl and the IstioOperator api"

[dhawton]

@dhawton any ideas on why the lint check is complaining about spelling here?

"Install Istio as primary in cluster1 using istioctl and the IstioOperator api"

Running locally (make lint) is easier to identify. It's because it's API not api.

[nshankar13]

/test doc.test.profile-default