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/tests/PnvPanel.Application.Tests/Auth/LoginCommandHandlerTests.cs

@@ -31,7 +31,10 @@ public class LoginCommandHandlerTests
             IsBlocked: false,
             MaxConfigs: 3,
             MaxIpLimit: RoleQuota.Unlimited,
-            SubscriptionToken: "sub-token"
+            SubscriptionToken: "sub-token",
+            BillingEnabled: false,
+            BillingPaidUntil: null,
+            BillingSuspended: false
         );
 
         _identityService