Gracefully handle errors in CreateOrderService

The following discussion from !506 should be addressed:

• @asubramanian1 started a discussion: (+1 comment)

  Wdyt about rescuing the operation, and returning { success: false }

  https://gitlab.com/gitlab-org/customers-gitlab-com/blob/24d53e03a63059232dcdc6931e25d21b3fe36841/app/services/create_order_service.rb#L27 and others could raise exception