Implement billing functionality and enhance role management

- Introduced billing capabilities, allowing users to request payments for subscription periods (3/6/12 months) with admin approval via Telegram.
- Updated role management to include a `BillingEnabled` property, preventing billing for admin roles.
- Enhanced the `CreateRoleCommand` and `UpdateRoleCommand` to accept billing parameters, ensuring proper handling during role creation and updates.
- Added new endpoints for billing management and integrated billing checks into VPN config creation to enforce payment requirements.
- Updated related services, models, and tests to support the new billing features, ensuring comprehensive coverage and functionality.
- Enhanced documentation to reflect the new billing processes and role management changes.

backend/src/PnvPanel.Infrastructure/DependencyInjection.cs

@@ -154,6 +154,7 @@ public static class DependencyInjection
         services.AddHostedService<TrafficSyncService>();
         services.AddHostedService<NodeHealthCheckService>();
         services.AddHostedService<TrafficRetentionService>();
+        services.AddHostedService<BillingService>();
 
         services.Configure<TelegramOptions>(configuration.GetSection(TelegramOptions.SectionName));