RELOPS-2375: Add SP3 dedicated host experiment

[jwmossmoz]

Summary

Adds temporary Azure Dedicated Host resources for the Windows Speedometer 3 GPU perf experiment pool.

This creates a host group and one host in the existing rg-west-us-3-gecko-t resource group for gecko-t/win11-64-25h2-gpu-perf-experiment. The host group enables automatic placement so the follow-up ARM template work can place Worker Manager-created VMs onto the host group.

Jira: https://mozilla-hub.atlassian.net/browse/RELOPS-2375
Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=2039391

Notes

azapi_resource is used for the host group and host because azurerm_dedicated_host currently rejects the Azure-supported NVadsA10v5_Type1 host SKU during provider-side validation.

The dedicated host quota in westus3 for StandardNVADSA10v5Family has been raised to 72 vCPUs for this single-host experiment.

Validation

• terraform -chdir=terraform/azure_fxci/gecko-t fmt -check
• terraform -chdir=terraform/azure_fxci/gecko-t validate
• User confirmed the Terraform apply worked after the quota bump.