Feature: add missing callbacks

[4nd2in]

• Add the following callbacks:
  • checkout.session.async_payment_failed
  • checkout.session.async_payment_succeeded
  • customer.subscription.paused
  • customer.subscription.pending_update_applied
  • customer.subscription.pending_update_expired
  • customer.subscription.resumed
  • invoice.deleted
  • invoice.finalization_failed
  • invoice.overdue
  • invoice.will_be_due
• Fix request handling in rack versions >= 3.1 where Request#[] is deprecated (#230)

[light-flight]

Great job! Waiting for your fix to be merged

[tansengming]

callbacks verified on https://docs.stripe.com/api/events/types