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: https://github.com/istio/istio.io/issues/14765

Tested against Istio 1.23.0-alpha.0 Helm charts.

Reviewers

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