Create Azure-based upgrade-to-cluster test script (escluster)

[cbaxley]

Part of: #737 (Eng Spec: Add clustering support for Elasticsearch)

Branch: cbaxley-737-implement-cluster

Description
As a tester, I want an Azure-based upgrade-to-cluster test script so that I can validate the upgrade path from a single-node LME installation to a multi-node Elasticsearch cluster.

Acceptance criteria

• Script exists at testing/v2/installers/cluster_installer/setup_upgrade_to_cluster.sh
• Script provisions multiple Azure VMs (default: 3)
• Script sets up SSH keys between local machine and all VMs
• Script clones LME repo and checks out specified branch on master
• Script installs single-node LME via install.sh on master
• Script verifies Elasticsearch is healthy before proceeding with upgrade
• Script copies SSH keys to root for ansible sudo operations
• Script creates cluster inventory with master node first
• Script runs convert_to_cluster.sh --skip-inventory --skip-prompts to upgrade to cluster
• Script outputs commands for SSH access, cluster health verification, and cleanup
• Script supports --debug flag for verbose ansible output