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.Api/Endpoints/RoleEndpoints.cs

@@ -53,7 +53,7 @@ public static class RoleEndpoints
     )
     {
         var result = await sender.Send(
-            new UpdateRoleCommand(id, body.MaxConfigs, body.MaxIpLimit),
+            new UpdateRoleCommand(id, body.MaxConfigs, body.MaxIpLimit, body.BillingEnabled),
             cancellationToken
         );
         return result.ToHttpResult();
@@ -84,6 +84,6 @@ public static class RoleEndpoints
     }
 }
 
-public sealed record UpdateRoleBody(int MaxConfigs, int MaxIpLimit);
+public sealed record UpdateRoleBody(int MaxConfigs, int MaxIpLimit, bool BillingEnabled);
 
 public sealed record ChangeUserRoleBody(Guid RoleId);