Refactor payment request handling to support role change top-ups

- Updated the `PaymentRequest` model to include a new `Kind` property, distinguishing between `Subscription` and `RoleChangeTopUp` requests.
- Modified the `TelegramNotifier` to accommodate the new request type, ensuring accurate notifications for role change top-ups.
- Enhanced the `ConfirmPaymentRequestCommandHandler` to handle role change top-ups without extending the billing period, reflecting the new payment logic.
- Updated various application components and tests to support the new payment request structure and ensure proper functionality.
- Revised API documentation to clarify the behavior of role change top-ups and their impact on billing.

backend/tests/PnvPanel.Application.Tests/Billing/MarkPaymentSent/MarkPaymentSentCommandHandlerTests.cs

@@ -41,6 +41,7 @@ public class MarkPaymentSentCommandHandlerTests
             .NotifyAdminsPaymentRequestedAsync(
                 request.Id,
                 Arg.Any<string>(),
+                PaymentRequestKind.Subscription,
                 PaymentPeriod.Year,
                 6000,
                 Arg.Any<CancellationToken>()