Push a message to RabbitMQ after user creation

[mdevrees]

After a new user is created, a message should be pushed to RabbitMQ through celery, the receiver of the message will be the CustomerService and it should only contain the newly created user email.

[mdevrees]

Create a task which only invokes celery.send_task(taskname, data). Make sure celery allows that task in celery_app.py. The invoke method should only push a message to rabbitmq (celery.send_task()) without having a method which also handles it. Call the invoke method using either .delay() or .apply_async()