[FEATURE REQ] Please add "FOCUS" param in CostDetailsMetricType

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/cost-management/resource-manager/Microsoft.CostManagement/stable/2025-03-01/costmanagement.generatecostdetailsreport.json#L192-L195

### API Spec version

2025-03-01

### Please describe the feature.

### Description of the new feature

Recently, it has become possible to retrieve FOCUS-compliant reports from Cost Management.
I want to retrieve Cost Management data in the FOCUS format using the Azure REST API.

### References:
- Microsoft official documentation: https://learn.microsoft.com/ja-jp/powershell/module/az.costmanagement/new-azcostmanagementdetailreport?view=azps-14.1.0
- FinOps Toolkit: https://microsoft.github.io/finops-toolkit/
- Improved Exports: https://learn.microsoft.com/en-us/azure/cost-management-billing/costs/tutorial-improved-exports
- https://github.com/Azure/azure-powershell/issues/28304

Open the linked costmanagement.generatecostdetailsreport.json specification at lines 192-195 and locate CostDetailsMetricType. Compare the 2025-03-01 definition with the referenced Azure Cost Management documentation and related issue. Done means the specification represents the FOCUS option and passes the repository's specification validation checks.

Written by the indexing model from the issue text.