refs https://github.com/TryGhost/Team/issues/1166
This will be handled by a payments module instead. In order to
disconnect Stripe we must delete all Stripe related data, which means an
Offer doesn't inherently have a stripe coupon id. Instead we can use a
payments service which will get/create the coupon for us when we need
it.
refs https://github.com/TryGhost/Members/commit/5172e40646
When we updated to use the OffersAPI instead of OfferRepository this was
missed, and we were passing blank coupon to Stripe Checkout. This should
eventually be replaced with a call like `getCoupon(offerId)` from a
payments service.
refs https://github.com/TryGhost/Team/issues/1131
- Includes `status` on OfferDTO so client can use it
- Allows editing `status` of Offers
- Allows setting initial `status` when creating Offers