Subscribe to newsletter

curl --request POST \
  --url https://staging.api.commercengine.io/api/v1/{store_id}/storefront/campaigns/newsletter-subscribe \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "email": "<string>"
}'

{
  "message": "<string>",
  "success": true
}