Fix build failure

Co-authored-by: Nipuni Kavindya <nipuni@entgra.io>
Co-committed-by: Nipuni Kavindya <nipuni@entgra.io>

components/application-mgt/io.entgra.device.mgt.core.application.mgt.core/src/main/java/io/entgra/device/mgt/core/application/mgt/core/util/subscription/mgt/SubscriptionManagementServiceProvider.java

@@ -33,6 +33,10 @@ public class SubscriptionManagementServiceProvider {
     private SubscriptionManagementServiceProvider() {
     }
 
+    public static SubscriptionManagementServiceProvider getInstance() {
+        return SubscriptionManagementProviderServiceHolder.INSTANCE;
+    }
+
     /**
      * Retrieves the appropriate SubscriptionManagementHelperService based on the provided SubscriptionInfo.
      *