Add subscription for a store events
This URL will be called by the server when the desired event will occur
Event name for the subscription
Subscription added
{"callbackUrl": "https://myserver.com/send/callback/here","eventName": "orderInProgress"}
{"subscriptionId": "AAA-123-BBB-456"}
{"orderId": "123","timestamp": "2018-10-19T16:46:45Z","status": "inProgress"}