feat(pay): one time payments

[tedbrine]

currently we only support subscriptions, would be good to look into one time purchases since it should be quite small

eg, ecom store

<Button
  onClick={async () => {
    const { paymentUrl } = await paykitClient.buy({
      productId: "xyz",
      successUrl: "/receipt",
      cancelUrl: "/basket",
    });
    if (paymentUrl) {
      window.location.href = paymentUrl;
    }
  }}
>
  Buy Product
</Button>

then we ideally have a custom on event which fires when we confirm a one time product is bought

could also extend metered usage by being able to top up a balance by paying

[linear]

PAY-191

[maxktz]

@t3duk, good call, I planned this initially and forgot make an issue

My thoughts on this:

• one-off checkouts with .checkout() and list of products
• some providers might not support subscriptions, but can still support one-off checkouts nice, so provider adapter will have capabilities[]

Products schema:

products[] becomes either plan() or product(), to support both plans and one-offs

not sure if we need pre-defined products tho, cause usually there is a lot, we can technically just pass them right into .checkout() at the time. Like a {price, name, description}[]

I'd probably start with pre-defined products, but better to implement dynamic ones also in future