Changes to the Payment Intent APIs for the next API version

[remi-stripe]

We are going to ship some changes to the Payment Intent APIs in the next API version. Though are fairly self-contained and pave the way for future changes. Changes are:

• status: remove require_source and require_source_action and add requires_payment_method and requires_action
• next_source_action renamed to next_action
• allowed_source_types renamed to payment_method_types
• authorize_with_url renamed to redirect_to_url both in the type of next action and in the hash that describes that next action.

cc @stripe/api-libraries @danwang-stripe

cc @mickjermsurawong-stripe To confirm naming for the new classes make sense (now that they are inline)

[mickjermsurawong-stripe]

@remi-stripe

• the payment NextAction, NextActionRedirectToUrl nested in PaymentIntent looks great with me.
  I see that in the the latest OpenAPI spec. (But client metadata is wrong, I will go and update it to reflect similarly this PR)
• Haven't seen the change on allowed_source_types in pay-server yet.
• We currently don't have enum on the status, so not sure if it's worth specifying that in comments. But that means we have to maintain the comment too which is inconsistent. I'm okay with what it is now.

[remi-stripe]

@mickjermsurawong-stripe thanks a lot for the review, this definitely helps vet the approach!

[remi-stripe]

@mickjermsurawong-stripe API version is going out tomorrow so marking this as ready to merge now that stripe-mock is updated and assigning to you for a full review.

[mickjermsurawong-stripe]

I think we need the additional field? At least it shows up in my autogen PR https://github.com/stripe/stripe-java/pull/676/files.. Also confirm that it's present in public OpenAPI

    Map<String, Object> useStripeSdk;

[remi-stripe]

@mickjermsurawong-stripe This is undocumented/secret right now though so not something we'd want to ship for now.

[remi-stripe]

Confirmed, we want the parameter/enum value but this property should not be in the libraries since it's opaque and specific to stripe.js

[mickjermsurawong-stripe]

ptal @remi-stripe, maybe we are missing a field on NextAction

[mickjermsurawong-stripe]

ah good to know.. Will make a PR to undocument that in pay-server.
LGTM