[AC-2488] Return default state for billing metadata when Organization has no Stripe entities (#4018)

* Return default state for billing metadata when no stripe entities

* Fix tests

src/Core/Billing/Models/OrganizationMetadataDTO.cs

@@ -1,4 +1,8 @@
 namespace Bit.Core.Billing.Models;
 
 public record OrganizationMetadataDTO(
-    bool IsOnSecretsManagerStandalone);
+    bool IsOnSecretsManagerStandalone)
+{
+    public static OrganizationMetadataDTO Default() => new(
+        IsOnSecretsManagerStandalone: default);
+}

src/Core/Billing/Queries/Implementations/OrganizationBillingQueries.cs

@@ -29,7 +29,7 @@ public class OrganizationBillingQueries(
 
         if (customer == null || subscription == null)
         {
-            return null;
+            return OrganizationMetadataDTO.Default();
         }
 
         var isOnSecretsManagerStandalone = IsOnSecretsManagerStandalone(organization, customer, subscription);