[Feature]: Please add "FOCUS" as a value for the Metric parameter in New-AzCostManagementDetailReport

### Description of the new feature

Recently, it has become possible to retrieve FOCUS-compliant reports from Cost Management.
I would like to be able to retrieve such reports with the `New-AzCostManagementDetailReport` cmdlet as well, by specifying "FOCUS" for the Metric parameter.

### 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

### Proposed implementation details (optional)

_No response_

Start at the New-AzCostManagementDetailReport cmdlet and inspect how the Metric parameter values are defined and validated. Compare its behavior with the linked Microsoft Cost Management documentation; done means the cmdlet accepts FOCUS as a Metric value and the applicable validation passes.

Written by the indexing model from the issue text.