Stripe: allow passing custom parameters to the Checkout session

packages/billing/core/src/schema/create-billing-checkout.schema.ts

@@ -15,4 +15,5 @@ export const CreateBillingCheckoutSchema = z.object({
       quantity: z.number(),
     }),
   ),
+  metadata: z.record(z.string()).optional(),
 });

packages/billing/stripe/src/services/create-stripe-checkout.ts

@@ -36,6 +36,7 @@ export async function createStripeCheckout(
         trial_period_days: params.plan.trialDays,
         metadata: {
           accountId: params.accountId,
+          ...(params.metadata ?? {}),
         },
       }
     : {};