feat: Replace interface{} with any type alias for improved code clarity

- Remove omitempty from Plan field in Subscriber model
- Update NotifySubscriberUpdate to use any instead of interface{}
- Update sendDeactivationRequest parameter type from interface{} to any

apps/api-server/internal/services/amf_client.go

@@ -87,7 +87,7 @@ func (a *AMFClient) TerminateSession(ctx context.Context, imsi models.IMSI, reas
 
 // NotifySubscriberUpdate notifies AMF of subscriber status changes
 func (a *AMFClient) NotifySubscriberUpdate(ctx context.Context, imsi models.IMSI, status models.SubscriberStatus) error {
-	req := map[string]interface{}{
+	req := map[string]any{
 		"imsi":      imsi,
 		"status":    status,
 		"timestamp": time.Now(),