Implement extension request and gift functionalities in billing system

- Added new endpoints for creating and managing extension requests, allowing users to request billing period extensions.
- Implemented admin approval processes for extension requests via Telegram, including inline buttons for approval and rejection.
- Introduced a gifting feature for admins to grant additional billing days directly to users without a request.
- Updated the support ticket model to accommodate extension requests and their associated properties.
- Enhanced the Telegram notifier to inform admins of new extension requests and notify users of approval or rejection.
- Updated frontend components to support the new extension request and gifting functionalities, including user interfaces for managing these features.
- Revised API documentation to reflect the new endpoints and their usage in the billing context.

backend/tests/PnvPanel.Domain.Tests/Support/SupportTicketTests.cs

@@ -45,6 +45,21 @@ public class SupportTicketTests
         Assert.Equal(3, ticket.ProposedMaxIpLimit);
     }
 
+    [Fact]
+    public void CreateExtensionRequest_SetsRequestedDays()
+    {
+        var userId = Guid.NewGuid();
+
+        var ticket = SupportTicket.CreateExtensionRequest(userId, 14);
+
+        Assert.Equal(userId, ticket.UserId);
+        Assert.Equal(TicketType.ExtensionRequest, ticket.Type);
+        Assert.Equal(TicketStatus.Open, ticket.Status);
+        Assert.Equal(14, ticket.RequestedDays);
+        Assert.Null(ticket.RequestedRoleId);
+        Assert.Null(ticket.ProposedRoleName);
+    }
+
     [Fact]
     public void Resolve_WhenOpen_SetsResolved()
     {