[Feature Request]: Support local/multiple currencies (e.g. GBP) in Arc Insights PBI Dashboards ESU cost forecasting

### Feature Type

- [ ] New Drop
- [x] Enhancement to an existing Drop
- [ ] Enhancement to the Jumpstart Drops website experience
- [ ] Something else

### Feature Description

The Arc Insights PBI Dashboards present ESU (Extended Security Update) cost forecasts and pricing in US Dollars (USD) only. This is a request to allow costs to be displayed in a user-selected local currency (for example GBP, EUR), so customers outside the US can read the figures directly without manual conversion.

### Motivation

The ESU Forecast is one of the most valuable views in this Drop - it helps customers estimate future Extended Security Update costs and prioritise modernisation/migration work. Global customers (for example, UK public sector organisations) need those figures in their local currency to make budget decisions and share numbers with finance teams. Today they have to mentally convert from USD, which reduces trust and slows decision-making. A customer specifically asked whether the dashboard costs can be shown in Pounds (GBP), which prompted this request.

### Proposed Solution

- Add a currency selector (e.g. a Power BI what-if parameter / slicer) with USD as the default and additional options such as GBP and EUR.
- Apply a configurable FX conversion rate to the USD price columns (software_esu_monthly and software_esu_yearly in dim_software_lifecycle.csv, and any USD-based figures in dim_azure_vm_skus.csv) and format the relevant measures/visuals with the selected currency symbol.
- Optionally document that Azure Arc ESU list prices are USD-based (per Azure Arc pricing) and explain how a user sets/updates the conversion rate.

### We need a URL from you

https://jumpstart.azure.com/azure_jumpstart_drops?drop=Arc%20Insights%20PBI%20Dashboards%20Powered%20by%20Jumpstart

### Additional Context

ESU pricing in this Drop is sourced from Azure Arc pricing, which is quoted in USD. The relevant reference data lives in ui_dashboard_workbook/arc_pbi_dashboard/artifacts/reference/dim_software_lifecycle.csv (columns software_esu_monthly / software_esu_yearly). A currency layer applied over these figures, with symbol-aware formatting in the visuals, would address the request. (Note: originally filed as #1909 via the CLI but auto-closed for not using the Issue Form; re-filing through the form here.)

### Code of Conduct and Licensing

- [x] I agree to follow this project's Code of Conduct and Licensing terms.

Start with the Arc Insights workbook and inspect ui_dashboard_workbook/arc_pbi_dashboard/artifacts/reference/dim_software_lifecycle.csv, including software_esu_monthly and software_esu_yearly; also check dim_azure_vm_skus.csv for other USD-based figures. Trace how these columns feed the ESU Forecast visuals, then verify that a selector, configurable FX rate, USD default, and currency-aware formatting produce local-currency forecasts.

Written by the indexing model from the issue text.