Add Admin Configuration to Restrict Available Countries Across the Storefront

Is your feature request related to a problem? Please describe.

The admin should have a configuration to select the countries where the store operates.

Only the countries selected by the admin should be available to customers throughout the storefront.

For example, if the admin enables only India and USA, customers should only see these two countries wherever a country selection is required.

Areas to Cover Customer registration Billing address Shipping address Checkout Customer account address Any other storefront form where customers can select a country

Describe the solution you'd like

Admin should be able to configure the allowed countries. Only the configured countries should be visible and selectable on the storefront. Non-configured countries should not appear in any country dropdown or country selection field. The restriction should apply consistently to registration, billing addresses, shipping addresses, checkout, and customer address management.

Describe alternatives you've considered

No response

Additional context

No response