Add way to use discountCode directly when creating a new checkout, without turning them first into discountId

[Igloczek]

it would be really helpful to be able to use discountCode instead of discountId while creating a new checkout

i'd say it's a common thing that you give user a URL to a pricing page with pre-populated discount code as a URL param, it's helpful either for support cases or some email campaign

none of this stuff should require to adjust app code, just to embed the discount IDs or doing some other shenanigans like keeping the copy of all discounts in own database

right now I'd have to ask for the discounts list every time someone wants to create a checkout, which isn't particularly fast, and in cases like mine, requires doing multiple requests just to get all discounts, because I have more than 100 of them

alternatively something like await polar.discounts.get({ discountCode }) will do too, but still more annoying to use than just dropping code while creating the checkout