Handle `charge.refund.updated` webhook event

[waiting-for-dev]

A refund can fail in certain situations, like for a closed bank account. See Stripe documentation for more information.

In that case, a charge.refund.updated event is published on Stripe. We need to listen to it and update Solidus counterpart. However, what we should do is unclear, as a Solidus refund doesn't have an associated state to mark as failed.