Allow stripe to collect billing address

[anuragphadnis2503]

All payments in foreign currencies require the billing address information to be collected, stripe allows to collect billing address collection in the checkout API. Since not everyone wants to save address in their database there are many use cases where this should be handled by stripe. For E.g. while using killbill only as a generic payment gateway.

I have added the parameter in the checkout API which can be set to allow billing address collection. The flag value is described in the stripe documentation here.