Support ISO 2 country codes in CountryFlag component and grid column.

1. src/component/CountryFlag.mjs:

   • Add countryCode_ reactive config.
   • Update afterSetLocation logic to prioritize countryCode for flag URL generation if available.
   • Use location for the text label.

2. src/grid/column/CountryFlag.mjs:

   • Add contentField config (defaulting to 'location').
   • Update applyRecordConfigs to map countryCode from the record if available.

3. apps/devindex/view/home/GridContainer.mjs:

   • Change the dataField for the 'Location' column from 'location' to 'country_code'.
   • Set sortable: false for this column.