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/Support/ListSelectableRoles/ListSelectableRolesQueryHandlerTests.cs

@@ -21,7 +21,10 @@ public class ListSelectableRolesQueryHandlerTests
             IsBlocked: false,
             MaxConfigs: 3,
             MaxIpLimit: 1,
-            SubscriptionToken: "token"
+            SubscriptionToken: "token",
+            BillingEnabled: false,
+            BillingPaidUntil: null,
+            BillingSuspended: false
         );
 
     [Fact]
@@ -37,9 +40,9 @@ public class ListSelectableRolesQueryHandlerTests
             .Returns(
                 new List<RoleDto>
                 {
-                    new(adminRoleId, "admin", -1, -1, IsSystem: true),
-                    new(currentRoleId, "user", 3, 1, IsSystem: true),
-                    new(extendedRoleId, "extended", 10, 5, IsSystem: false),
+                    new(adminRoleId, "admin", -1, -1, IsSystem: true, BillingEnabled: false),
+                    new(currentRoleId, "user", 3, 1, IsSystem: true, BillingEnabled: false),
+                    new(extendedRoleId, "extended", 10, 5, IsSystem: false, BillingEnabled: false),
                 }
             );
         _identityService
@@ -71,8 +74,8 @@ public class ListSelectableRolesQueryHandlerTests
             .Returns(
                 new List<RoleDto>
                 {
-                    new(adminRoleId, "admin", -1, -1, IsSystem: true),
-                    new(userRoleId, "user", 3, 1, IsSystem: true),
+                    new(adminRoleId, "admin", -1, -1, IsSystem: true, BillingEnabled: false),
+                    new(userRoleId, "user", 3, 1, IsSystem: true, BillingEnabled: false),
                 }
             );
         _identityService