fix: platform onboarding improvements (#15053)

* allow stripe to display promo codes option

* fix layout issues for tablet devices

* redirect platform users to new platform onboarding

apps/api/v2/src/modules/billing/services/billing.service.ts

@@ -75,6 +75,7 @@ export class BillingService {
             plan: plan.toString(),
           },
         },
+        allow_promotion_codes: true,
       });
 
       if (!url) throw new InternalServerErrorException("Failed to create Stripe session.");