fix: ensure metadata key is always present in BOOKING_CREATED webhook payload (#27300)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: ali@cal.com <ali@cal.com>
Co-authored-by: Morgan <33722304+ThyMinimalDev@users.noreply.github.com>

packages/features/bookings/lib/handleConfirmation.ts

@@ -577,7 +577,7 @@ export async function handleConfirmation(args: {
       eventTypeId: eventType?.id,
       status: "ACCEPTED",
       smsReminderNumber: booking.smsReminderNumber || undefined,
-      metadata: meetingUrl ? { videoCallUrl: meetingUrl } : undefined,
+      metadata: meetingUrl ? { videoCallUrl: meetingUrl } : {},
       ...(platformClientParams ? platformClientParams : {}),
     };